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/service/post_service.go

@@ -2,7 +2,6 @@ package service
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"log"
 	"math/rand"
@@ -12,6 +11,7 @@ import (
 	"carrot_bbs/internal/cache"
 	"carrot_bbs/internal/model"
 	"carrot_bbs/internal/pkg/gorse"
+	"carrot_bbs/internal/pkg/hook"
 	"carrot_bbs/internal/repository"
 )
 
@@ -73,10 +73,10 @@ type postServiceImpl struct {
 	postAIService        *PostAIService
 	txManager            repository.TransactionManager
 	logService           *LogService
+	hookManager          *hook.Manager
 }
 
-// NewPostService 创建帖子服务
-func NewPostService(postRepo *repository.PostRepository, systemMessageService SystemMessageService, gorseClient gorse.Client, postAIService *PostAIService, cacheBackend cache.Cache, txManager repository.TransactionManager) PostService {
+func NewPostService(postRepo *repository.PostRepository, systemMessageService SystemMessageService, gorseClient gorse.Client, postAIService *PostAIService, cacheBackend cache.Cache, txManager repository.TransactionManager, hookManager *hook.Manager) PostService {
 	return &postServiceImpl{
 		postRepo:             postRepo,
 		systemMessageService: systemMessageService,
@@ -85,6 +85,7 @@ func NewPostService(postRepo *repository.PostRepository, systemMessageService Sy
 		postAIService:        postAIService,
 		txManager:            txManager,
 		logService:           nil,
+		hookManager:          hookManager,
 	}
 }
 
@@ -147,40 +148,48 @@ func (s *postServiceImpl) reviewPostAsync(postID, userID, title, content string,
 		}
 	}()
 
-	// 未启用AI时，直接发布
-	if s.postAIService == nil || !s.postAIService.IsEnabled() {
+	if s.hookManager == nil {
 		if err := s.updateModerationStatusWithRetry(postID, model.PostStatusPublished, "", "system"); err != nil {
-			log.Printf("[WARN] Failed to publish post without AI moderation: %v", err)
+			log.Printf("[WARN] Failed to publish post without hook manager: %v", err)
 		} else {
 			s.invalidatePostCaches(postID)
 		}
 		return
 	}
 
-	err := s.postAIService.ModeratePost(context.Background(), title, content, images)
-	if err != nil {
-		var rejectedErr *PostModerationRejectedError
-		if errors.As(err, &rejectedErr) {
-			if updateErr := s.updateModerationStatusWithRetry(postID, model.PostStatusRejected, rejectedErr.UserMessage(), "ai"); updateErr != nil {
-				log.Printf("[WARN] Failed to reject post %s: %v", postID, updateErr)
-			} else {
-				s.invalidatePostCaches(postID)
-			}
-			s.notifyModerationRejected(userID, rejectedErr.Reason)
-			return
-		}
+	var authorID uint
+	fmt.Sscanf(userID, "%d", &authorID)
 
-		// 规则审核不可用时，降级为发布，避免长时间pending
-		if updateErr := s.updateModerationStatusWithRetry(postID, model.PostStatusPublished, "", "system"); updateErr != nil {
-			log.Printf("[WARN] Failed to publish post %s after moderation error: %v", postID, updateErr)
+	result := &hook.ModerationResult{}
+	s.hookManager.TriggerWithMetadata(context.Background(), hook.HookPostPreModerate, authorID, &hook.PostModerateHookData{
+		PostID:   postID,
+		Title:    title,
+		Content:  content,
+		Images:   images,
+		AuthorID: authorID,
+	}, map[string]interface{}{
+		"result": result,
+	})
+
+	s.hookManager.Trigger(context.Background(), hook.HookPostModerated, authorID, &hook.PostModeratedHookData{
+		PostID:       postID,
+		AuthorID:     authorID,
+		Approved:     result.Approved,
+		RejectReason: result.RejectReason,
+		ReviewedBy:   result.ReviewedBy,
+	})
+
+	if !result.Approved {
+		if updateErr := s.updateModerationStatusWithRetry(postID, model.PostStatusRejected, result.RejectReason, result.ReviewedBy); updateErr != nil {
+			log.Printf("[WARN] Failed to reject post %s: %v", postID, updateErr)
 		} else {
 			s.invalidatePostCaches(postID)
 		}
-		log.Printf("[WARN] Post moderation failed, fallback publish post=%s err=%v", postID, err)
+		s.notifyModerationRejected(userID, result.RejectReason)
 		return
 	}
 
-	if err := s.updateModerationStatusWithRetry(postID, model.PostStatusPublished, "", "ai"); err != nil {
+	if err := s.updateModerationStatusWithRetry(postID, model.PostStatusPublished, "", result.ReviewedBy); err != nil {
 		log.Printf("[WARN] Failed to publish post %s: %v", postID, err)
 		return
 	}