修复 LLM Provider 配置热更新问题

问题：在 /admin/llm/api 页面修改 AI 提供商配置后，配置没有立即生效，AI 依然使用旧的提供商工作

根本原因：
- LLM Provider 配置在程序启动时加载到内存 (llm.State)
- 管理后台修改配置时，只更新了数据库，内存配置未更新
- AI 继续使用内存中的旧配置

解决方案：
1. 为 llm.State 添加动态更新方法 (UpdateProvider/AddProvider/RemoveProvider)
2. 在 AI Service 中暴露配置更新接口，支持运行时重新加载
3. 在配置保存后自动触发内存配置重新加载
4. 创建新的 LLM Client 使新配置立即生效

关键特性：
- 线程安全：使用 sync.RWMutex 保护并发访问
- 容错处理：重新加载失败不影响数据库更新
- 无需重启：配置修改后立即生效
- 完整测试：添加单元测试验证功能

修改文件：
- internal/llm/state.go: 添加配置更新方法
- internal/ai/service.go: 添加配置重新加载接口
- internal/llmadmin/admin_llm_routes.go: 配置更新时触发重新加载
- internal/web/web.go: 传递 AI Service 到路由
- main.go: 连接组件
- internal/llm/state_test.go: 新增单元测试
- internal/web/map_tile_proxy_routes_test.go: 修复测试

测试：
- ✅ 所有现有测试通过
- ✅ 新增测试覆盖核心功能
- ✅ 项目成功编译

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

internal/web/web.go

@@ -27,10 +27,17 @@ import (
 	"meshtastic_mqtt_server/internal/webutil"
 )
 
-func NewHTTPServer(cfg configpkg.WebConfig, consoleLog bool, store *storepkg.Store, sessions *auth.Manager, mqttStatus MQTTStatusProvider, blocking *blockingpkg.Cache, forwarder mqttforwardpkg.Reloader, settings *rspkg.Cache, botSender botpkg.TextSender) *http.Server {
+// LLMProviderReloader is the interface for reloading LLM provider configuration
+type LLMProviderReloader interface {
+	ReloadLLMProvider(config interface{}) error
+	AddLLMProvider(config interface{}) error
+	RemoveLLMProvider(name string) error
+}
+
+func NewHTTPServer(cfg configpkg.WebConfig, consoleLog bool, store *storepkg.Store, sessions *auth.Manager, mqttStatus MQTTStatusProvider, blocking *blockingpkg.Cache, forwarder mqttforwardpkg.Reloader, settings *rspkg.Cache, botSender botpkg.TextSender, aiService LLMProviderReloader) *http.Server {
 	return &http.Server{
 		Addr:    net.JoinHostPort(cfg.Host, strconv.Itoa(cfg.Port)),
-		Handler: NewRouter(cfg, consoleLog, store, sessions, mqttStatus, blocking, forwarder, settings, botSender),
+		Handler: NewRouter(cfg, consoleLog, store, sessions, mqttStatus, blocking, forwarder, settings, botSender, aiService),
 	}
 }
 
@@ -60,7 +67,7 @@ func ServeUnixSocket(server *http.Server, socketPath string) error {
 	return server.Serve(listener)
 }
 
-func NewRouter(cfg configpkg.WebConfig, consoleLog bool, store *storepkg.Store, sessions *auth.Manager, mqttStatus MQTTStatusProvider, blocking *blockingpkg.Cache, forwarder mqttforwardpkg.Reloader, settings *rspkg.Cache, botSender botpkg.TextSender) *gin.Engine {
+func NewRouter(cfg configpkg.WebConfig, consoleLog bool, store *storepkg.Store, sessions *auth.Manager, mqttStatus MQTTStatusProvider, blocking *blockingpkg.Cache, forwarder mqttforwardpkg.Reloader, settings *rspkg.Cache, botSender botpkg.TextSender, aiService LLMProviderReloader) *gin.Engine {
 	r := gin.New()
 	if consoleLog {
 		r.Use(gin.Logger(), gin.Recovery())
@@ -69,7 +76,7 @@ func NewRouter(cfg configpkg.WebConfig, consoleLog bool, store *storepkg.Store,
 	}
 	api := r.Group("/api")
 	registerAPIRoutes(api, store, cfg.MapTileCacheDir)
-	registerAdminRoutes(api.Group("/admin"), store, sessions, mqttStatus, blocking, forwarder, settings, botSender)
+	registerAdminRoutes(api.Group("/admin"), store, sessions, mqttStatus, blocking, forwarder, settings, botSender, aiService)
 	registerStaticRoutes(r, cfg.StaticDir)
 	return r
 }
@@ -163,7 +170,7 @@ func registerAPIRoutes(r gin.IRouter, store *storepkg.Store, mapTileCacheDir str
 	})
 }
 
-func registerAdminRoutes(r gin.IRouter, store *storepkg.Store, sessions *auth.Manager, mqttStatus MQTTStatusProvider, blocking *blockingpkg.Cache, forwarder mqttforwardpkg.Reloader, settings *rspkg.Cache, botSender botpkg.TextSender) {
+func registerAdminRoutes(r gin.IRouter, store *storepkg.Store, sessions *auth.Manager, mqttStatus MQTTStatusProvider, blocking *blockingpkg.Cache, forwarder mqttforwardpkg.Reloader, settings *rspkg.Cache, botSender botpkg.TextSender, aiService LLMProviderReloader) {
 	type loginRequest struct {
 		Username string `json:"username"`
 		Password string `json:"password"`
@@ -230,7 +237,7 @@ func registerAdminRoutes(r gin.IRouter, store *storepkg.Store, sessions *auth.Ma
 	mappkg.RegisterAdminRoutes(protected, store)
 	helppkg.RegisterAdminRoutes(protected, store)
 	botpkg.RegisterRoutes(protected, store, botSender)
-	llmadminpkg.RegisterRoutes(protected, store)
+	llmadminpkg.RegisterRoutes(protected, store, aiService)
 	protected.GET("/me", func(c *gin.Context) {
 		claims := c.MustGet("admin_claims").(*auth.SessionClaims)
 		c.JSON(http.StatusOK, gin.H{"user": auth.AdminUserDTO{Username: claims.Username, Role: claims.Role}})