feat: add hook system, QR code login, and layered cache

- Implement extensible hook system for content moderation with
  builtin and AI-powered moderation hooks
- Add QR code login feature with SSE for real-time status updates
  and scan/confirm/cancel workflow
- Introduce layered cache with local LRU + Redis backend for
  improved read performance
- Refactor post and comment services to use hook-based moderation
  instead of direct AI service calls
- Add local cache configuration options (size, buckets, ttl)

internal/model/login_log.go

@@ -47,6 +47,7 @@ const (
 	LoginTypeSMS      LoginType = "sms"
 	LoginTypeEmail    LoginType = "email"
 	LoginTypeOAuth    LoginType = "oauth"
+	LoginTypeQRCode   LoginType = "qrcode"
 )
 
 // LoginMethod 登录方式