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/wire/handler.go

@@ -28,6 +28,7 @@ var HandlerSet = wire.NewSet(
 	handler.NewAdminGroupHandler,
 	handler.NewAdminDashboardHandler,
 	handler.NewAdminLogHandler,
+	handler.NewQRCodeHandler,
 
 	// 需要特殊处理的 Handler
 	ProvideUserHandler,