feat: 管理后台一键从 Caddy 获取证书 + TLS 证书热加载

- 域名编辑页新增“从 Caddy 获取证书”按钮：一键把本机 Caddy 已签发的
  证书与私钥导入该域名的 TLS 目录并自动启用 TLS，支持通配符证书
  （如 *.example.com 可匹配 mail.example.com），成功/失败均回显横幅
- 新增 internal/caddycert：搜索 Caddy 证书存储（同步镜像目录优先、
  caddy.data_dir 与常见位置兜底），校验密钥对/有效期/SAN，并给出
  可操作的中文错误提示（未找到/证书无效/权限不足）
- install.sh 新增 setup-caddy-cert：安装 root 权限的 systemd
  path+timer 同步任务（mailgo-caddy-sync），把 Caddy 证书树镜像到
  /srv/mail_go/tls/caddy（证书续期后自动更新、每日兜底），另授予
  ACL 作为直接读取兜底；install 时自动检测并配置
- 新增 [caddy] data_dir 配置节，支持自定义 Caddy 数据目录
- 新增 internal/tlsutil：TLS 证书热加载器，每次握手按需重载证书
  文件（mtime 检测），重载失败继续使用旧证书兜底并节流重试；
  应用于 SMTPS 465/IMAPS 993/POP3S 995 与 STARTTLS，导入或上传
  新证书后无需重启服务即生效
- 证书来源动态切换：协议显式配置优先，否则取首个启用 TLS 且有证书
  的域名（10 秒缓存），新域名一键导入证书后自动切换
- 更新 README 与界面文案（去掉“重启服务生效”提示）

internal/web/handlers/admin.go

@@ -5,12 +5,14 @@ import (
 	"fmt"
 	"log"
 	"net/http"
+	"net/url"
 	"os"
 	"path/filepath"
 	"strconv"
 	"strings"
 	"time"
 
+	"mail_go/internal/caddycert"
 	"mail_go/internal/db"
 	"mail_go/internal/dkim"
 	"mail_go/internal/outbound"
@@ -23,16 +25,17 @@ import (
 
 // AdminHandler handles admin-related routes (dashboard, domain/user management).
 type AdminHandler struct {
-	stores   *store.Stores
-	storage  *storage.AttachmentStorage
-	tlsDir   string
-	outbound *outbound.Manager
+	stores       *store.Stores
+	storage      *storage.AttachmentStorage
+	tlsDir       string
+	caddyDataDir string
+	outbound     *outbound.Manager
 }
 
 // NewAdminHandler creates a new AdminHandler with the given stores, attachment
-// storage, TLS directory and outbound delivery manager.
-func NewAdminHandler(stores *store.Stores, attStorage *storage.AttachmentStorage, tlsDir string, ob *outbound.Manager) *AdminHandler {
-	return &AdminHandler{stores: stores, storage: attStorage, tlsDir: tlsDir, outbound: ob}
+// storage, TLS directory, Caddy data directory and outbound delivery manager.
+func NewAdminHandler(stores *store.Stores, attStorage *storage.AttachmentStorage, tlsDir string, caddyDataDir string, ob *outbound.Manager) *AdminHandler {
+	return &AdminHandler{stores: stores, storage: attStorage, tlsDir: tlsDir, caddyDataDir: caddyDataDir, outbound: ob}
 }
 
 // Dashboard renders the admin dashboard with summary statistics.
@@ -209,6 +212,16 @@ func (h *AdminHandler) EditDomain(c *gin.Context) {
 	}
 
 	currentUser, _ := c.Get("currentUser")
+
+	caddyMsg, caddyMsgType := "", ""
+	if c.Query("caddy_err") != "" {
+		caddyMsg = c.Query("caddy_err")
+		caddyMsgType = "error"
+	} else if c.Query("caddy_ok") == "1" {
+		caddyMsg = "✅ 已从 Caddy 获取证书并保存到域名 TLS 目录，同时已启用该域名的 TLS；证书已热加载，无需重启服务。"
+		caddyMsgType = "success"
+	}
+
 	c.HTML(200, "admin_domain_form", gin.H{
 		"currentUser":       currentUser,
 		"activeFolder":      "domains",
@@ -217,6 +230,8 @@ func (h *AdminHandler) EditDomain(c *gin.Context) {
 		"domain":            domain,
 		"tlsPublicCert":     readTLSCert(domain.TlsCertPath),
 		"tlsCertConfigured": domain.TlsCertPath != "" && domain.TlsKeyPath != "",
+		"caddyMsg":          caddyMsg,
+		"caddyMsgType":      caddyMsgType,
 	})
 }
 
@@ -264,6 +279,78 @@ func (h *AdminHandler) UpdateDomain(c *gin.Context) {
 	c.Redirect(http.StatusFound, "/admin/domains")
 }
 
+// FetchCaddyCert 尝试从本机 Caddy 的证书存储中获取该域名的证书与私钥，
+// 保存到 MailGo 的域名 TLS 目录并更新数据库记录。结果通过查询参数回显到
+// 编辑页面（caddy_ok=1 成功 / caddy_err=<消息> 失败）。
+func (h *AdminHandler) FetchCaddyCert(c *gin.Context) {
+	id, err := strconv.ParseUint(c.Param("id"), 10, 64)
+	if err != nil {
+		c.String(http.StatusBadRequest, "无效的域名ID")
+		return
+	}
+
+	domain, err := h.stores.Domains.GetByID(uint(id))
+	if err != nil {
+		c.String(http.StatusNotFound, "域名不存在")
+		return
+	}
+
+	editURL := fmt.Sprintf("/admin/domains/%d/edit", domain.ID)
+	fail := func(msg string) {
+		log.Printf("从 Caddy 获取证书失败 domain=%s: %s", domain.Name, msg)
+		c.Redirect(http.StatusFound, editURL+"?caddy_err="+url.QueryEscape(msg))
+	}
+
+	cert, err := caddycert.Fetch(domain.Name, h.caddyCertRoots())
+	if err != nil {
+		fail(fmt.Sprintf("从 Caddy 获取证书失败: %v", err))
+		return
+	}
+
+	// 保存到域名 TLS 目录（与手动上传证书的位置一致）
+	domainTLSDir := filepath.Join(h.tlsDir, strconv.FormatUint(uint64(domain.ID), 10))
+	if err := os.MkdirAll(domainTLSDir, 0700); err != nil {
+		fail(fmt.Sprintf("创建 TLS 证书目录失败: %v", err))
+		return
+	}
+
+	certPath := filepath.Join(domainTLSDir, "cert.pem")
+	keyPath := filepath.Join(domainTLSDir, "key.pem")
+	if err := os.WriteFile(certPath, cert.CertPEM, 0644); err != nil {
+		fail(fmt.Sprintf("保存 TLS 公钥证书失败: %v", err))
+		return
+	}
+	if err := os.WriteFile(keyPath, cert.KeyPEM, 0600); err != nil {
+		fail(fmt.Sprintf("保存 TLS 私钥失败: %v", err))
+		return
+	}
+
+	domain.TlsCertPath = certPath
+	domain.TlsKeyPath = keyPath
+	domain.TlsEnabled = true
+	if err := h.stores.Domains.Update(domain); err != nil {
+		fail(fmt.Sprintf("更新域名记录失败: %v", err))
+		return
+	}
+
+	log.Printf("已从 Caddy 导入域名 %s 的证书 (%s)，热加载生效", domain.Name, cert.Source)
+	c.Redirect(http.StatusFound, editURL+"?caddy_ok=1")
+}
+
+// caddyCertRoots 返回按优先级排列的证书来源目录：
+//  1. MailGo 的同步镜像目录 <storage>/tls/caddy —— 由 install.sh 安装的
+//     systemd path 同步任务以 root 权限从 Caddy 证书存储镜像而来，
+//     mail_go 始终可读，证书续期后自动更新；
+//  2. 配置文件 caddy.data_dir 指定的目录（可选）；
+//
+// 其余默认位置由 caddycert.Fetch 自行探测。
+func (h *AdminHandler) caddyCertRoots() []string {
+	return []string{
+		filepath.Join(filepath.Dir(h.tlsDir), "caddy"),
+		h.caddyDataDir,
+	}
+}
+
 func readTLSCert(path string) string {
 	if path == "" {
 		return ""

internal/web/server.go

@@ -38,14 +38,15 @@ func formatBytes(b int64) string {
 
 // WebServer wraps the Gin engine and its dependencies.
 type WebServer struct {
-	engine     *gin.Engine
-	stores     *store.Stores
-	storage    *storage.AttachmentStorage
-	cfg        config.WebConfig
-	storageCfg config.StorageConfig
-	authCfg    config.AuthConfig
-	banCfg     config.BanConfig
-	outbound   *outbound.Manager
+	engine       *gin.Engine
+	stores       *store.Stores
+	storage      *storage.AttachmentStorage
+	cfg          config.WebConfig
+	storageCfg   config.StorageConfig
+	authCfg      config.AuthConfig
+	banCfg       config.BanConfig
+	caddyDataDir string
+	outbound     *outbound.Manager
 }
 
 // templateFuncs returns custom template functions for rendering.
@@ -84,7 +85,7 @@ func templateFuncs() template.FuncMap {
 
 // NewWebServer creates a new WebServer, initializes the Gin engine,
 // configures sessions, middleware, and registers all routes.
-func NewWebServer(cfg config.WebConfig, stores *store.Stores, attStorage *storage.AttachmentStorage, storageCfg config.StorageConfig, authCfg config.AuthConfig, banCfg config.BanConfig, ob *outbound.Manager) *WebServer {
+func NewWebServer(cfg config.WebConfig, stores *store.Stores, attStorage *storage.AttachmentStorage, storageCfg config.StorageConfig, authCfg config.AuthConfig, banCfg config.BanConfig, caddyCfg config.CaddyConfig, ob *outbound.Manager) *WebServer {
 	gin.SetMode(gin.ReleaseMode)
 	engine := gin.New()
 	engine.Use(gin.Logger())
@@ -107,14 +108,15 @@ func NewWebServer(cfg config.WebConfig, stores *store.Stores, attStorage *storag
 	engine.SetHTMLTemplate(tmpl)
 
 	ws := &WebServer{
-		engine:     engine,
-		stores:     stores,
-		storage:    attStorage,
-		cfg:        cfg,
-		storageCfg: storageCfg,
-		authCfg:    authCfg,
-		banCfg:     banCfg,
-		outbound:   ob,
+		engine:       engine,
+		stores:       stores,
+		storage:      attStorage,
+		cfg:          cfg,
+		storageCfg:   storageCfg,
+		authCfg:      authCfg,
+		banCfg:       banCfg,
+		caddyDataDir: caddyCfg.DataDir,
+		outbound:     ob,
 	}
 
 	ws.registerRoutes()
@@ -125,7 +127,7 @@ func NewWebServer(cfg config.WebConfig, stores *store.Stores, attStorage *storag
 func (ws *WebServer) registerRoutes() {
 	authHandler := handlers.NewAuthHandler(ws.stores, ws.authCfg, ws.banCfg)
 	mailHandler := handlers.NewMailHandler(ws.stores, ws.storage, ws.outbound)
-	adminHandler := handlers.NewAdminHandler(ws.stores, ws.storage, filepath.Join(ws.storageCfg.BaseDir, "tls", "domains"), ws.outbound)
+	adminHandler := handlers.NewAdminHandler(ws.stores, ws.storage, filepath.Join(ws.storageCfg.BaseDir, "tls", "domains"), ws.caddyDataDir, ws.outbound)
 
 	// Apply BanMiddleware globally before public routes
 	ws.engine.Use(middleware.BanMiddleware(ws.stores))
@@ -175,6 +177,7 @@ func (ws *WebServer) registerRoutes() {
 		admin.GET("/domains/:id/edit", adminHandler.EditDomain)
 		admin.POST("/domains/:id", adminHandler.UpdateDomain)
 		admin.POST("/domains/:id/delete", adminHandler.DeleteDomain)
+		admin.POST("/domains/:id/fetch-caddy-cert", adminHandler.FetchCaddyCert)
 		admin.GET("/domains/:id/dns", adminHandler.DNSHint)
 		admin.GET("/users", adminHandler.ListUsers)
 		admin.GET("/users/new", adminHandler.NewUser)

internal/web/templates/admin/domain_form.html

@@ -24,6 +24,7 @@
                 <div class="card">
                     <h2 style="margin-bottom:16px;">{{if .isEdit}}编辑域名{{else}}新增域名{{end}}</h2>
                     {{if .error}}<div class="alert alert-error">{{.error}}</div>{{end}}
+                    {{if .caddyMsg}}<div class="alert {{if eq .caddyMsgType "success"}}alert-success{{else}}alert-error{{end}}">{{.caddyMsg}}</div>{{end}}
                     <form method="POST" action="{{if .isEdit}}/admin/domains/{{.domain.ID}}{{else}}/admin/domains{{end}}">
                         <div class="form-group">
                             <label>域名</label>
@@ -63,12 +64,40 @@
                                 <label>TLS 公钥证书 PEM</label>
                                 <textarea name="tls_public_cert" rows="8" placeholder="-----BEGIN CERTIFICATE-----&#10;...&#10;-----END CERTIFICATE-----" style="font-family:monospace;">{{.tlsPublicCert}}</textarea>
                                 {{if .tlsCertConfigured}}
-                                <p style="color:#27ae60;font-size:12px;margin-top:4px;">✅ TLS 证书已配置；上传新证书后需重启服务生效。</p>
+                                <p style="color:#27ae60;font-size:12px;margin-top:4px;">✅ TLS 证书已配置；上传新证书后自动热加载生效。</p>
                                 {{else}}
                                 <p style="color:#e67e22;font-size:12px;margin-top:4px;">⚠️ TLS 证书未配置，启用 TLS 时必须同时填写私钥和证书。</p>
                                 {{end}}
                             </div>
                         </div>
+                        <div class="form-group" style="margin-top:4px;">
+                            <label>从 Caddy 获取证书</label>
+                            <p style="color:#7f8c8d;font-size:12px;margin-top:2px;margin-bottom:8px;">若该域名已由本机 Caddy 托管 HTTPS（自动签发证书），可一键导入其证书与私钥，并自动启用 TLS；证书热加载，无需重启服务。</p>
+                            <button type="button" class="btn" id="btn_fetch_caddy" onclick="fetchCaddyCert()" style="background:#2e86de;color:#fff;">🔒 从 Caddy 获取证书</button>
+                            <span id="caddy_fetch_msg" style="margin-left:10px;font-size:12px;color:#7f8c8d;"></span>
+                            <script>
+                            async function fetchCaddyCert() {
+                                var btn = document.getElementById('btn_fetch_caddy');
+                                var msg = document.getElementById('caddy_fetch_msg');
+                                btn.disabled = true;
+                                var oldText = btn.textContent;
+                                btn.textContent = '获取中…';
+                                msg.textContent = '';
+                                try {
+                                    var resp = await fetch('/admin/domains/{{.domain.ID}}/fetch-caddy-cert', { method: 'POST' });
+                                    if (resp.redirected) {
+                                        window.location.href = resp.url;
+                                        return;
+                                    }
+                                    msg.textContent = '获取失败: ' + await resp.text();
+                                } catch (e) {
+                                    msg.textContent = '请求失败: ' + e;
+                                }
+                                btn.disabled = false;
+                                btn.textContent = oldText;
+                            }
+                            </script>
+                        </div>
                         {{end}}
                         <script>
                         function togglePorts() {