feat: 新增 SMTP/IMAP/POP3 协议调用日志（含攻击分析筛选）

- 每个连接记录一条日志：协议、端口、来源 IP、用户名、成功/失败、
  失败原因（密码错误/IP封禁/中继被拒/发件人伪造/未认证发信等）、
  操作摘要、消息数与会话时长
- 管理后台新增「协议日志」页：按协议/状态/IP/用户名/时间筛选，
  今日与历史成功/失败统计卡片，分页查看，可手动清理
- 后台每 6 小时自动清理超出 protocol_log_keep_days（默认30天）
  的日志；新增 [web] protocol_log_keep_days 配置项
- 修复 POP3 认证既有 bug：handleUSER 丢弃邮箱域名导致 PASS 永远失败
- 新增 store 单测、SMTP/POP3 端到端测试与模板渲染测试

internal/store/stores.go

@@ -8,23 +8,25 @@ import (
 
 // Stores aggregates all store interfaces for convenient access.
 type Stores struct {
-	Users       UserStore
-	Mails       MailStore
-	Domains     DomainStore
-	Attachments AttachmentStore
-	Bans        BanStore
-	Outbound    OutboundStore
+	Users        UserStore
+	Mails        MailStore
+	Domains      DomainStore
+	Attachments  AttachmentStore
+	Bans         BanStore
+	Outbound     OutboundStore
+	ProtocolLogs ProtocolLogStore
 }
 
 // NewStores creates a new Stores instance with all GORM-backed implementations.
 func NewStores(database *gorm.DB) *Stores {
 	return &Stores{
-		Users:       newUserStore(database),
-		Mails:       newMailStore(database),
-		Domains:     newDomainStore(database),
-		Attachments: newAttachmentStore(database),
-		Bans:        newBanStore(database),
-		Outbound:    newOutboundStore(database),
+		Users:        newUserStore(database),
+		Mails:        newMailStore(database),
+		Domains:      newDomainStore(database),
+		Attachments:  newAttachmentStore(database),
+		Bans:         newBanStore(database),
+		Outbound:     newOutboundStore(database),
+		ProtocolLogs: newProtocolLogStore(database),
 	}
 }
 
@@ -34,3 +36,4 @@ var _ = db.Domain{}
 var _ = db.Message{}
 var _ = db.Attachment{}
 var _ = db.BanEntry{}
+var _ = db.ProtocolLog{}