refactor: cleanup unused code and simplify internal packages

This commit performs a significant cleanup of the codebase by removing unused functions, methods, and entire files across various internal modules. This reduces technical debt and simplifies the project structure.

Key changes include:
- **cache**: Removed unused cache key generators and metrics snapshots.
- **dto**: Removed redundant converter functions and segment creation helpers.
- **middleware**: Deleted the unused `logger.go` middleware and simplified `ratelimit.go` and `casbin.go`.
- **model**: Removed unused ID helpers, database closing functions, and batch decryption logic.
- **pkg**: Cleaned up unused utility functions in `circuitbreaker`, `crypto`, `cursor`, `hook`, and `utils`.
- **service**: Deleted `account_cleanup_service.go` and removed unused helper functions in `log_cleanup_service.go` and `sensitive_service.go`.
- **repository**: Removed unused private loading methods in `comment_repo.go`.

internal/model/message.go

@@ -303,76 +303,6 @@ func (m *Message) IsInteractionNotification() bool {
 	}
 }
 
-// BatchDecryptMessages 批量并行解密消息
-// 用于批量查询后提高解密性能，比逐条调用 AfterFind 更高效
-// workerCount 指定并行工作数，如果 <= 0 则使用默认值
-func BatchDecryptMessages(messages []*Message, workerCount int) error {
-	if len(messages) == 0 {
-		return nil
-	}
-
-	encryptor := crypto.GetMessageEncryptor()
-	if encryptor == nil {
-		// 加密器未初始化，直接解析 JSON（兼容模式）
-		for _, m := range messages {
-			if m.decrypted || m.SegmentsEncrypted == "" {
-				m.decrypted = true
-				continue
-			}
-			if err := json.Unmarshal([]byte(m.SegmentsEncrypted), &m.Segments); err != nil {
-				return err
-			}
-			m.decrypted = true
-		}
-		return nil
-	}
-
-	// 小批量直接串行处理
-	if len(messages) <= 10 {
-		for _, m := range messages {
-			if err := m.decryptSegments(); err != nil {
-				return err
-			}
-		}
-		return nil
-	}
-
-	// 并行解密
-	// 先收集需要解密的密文
-	ciphertexts := make([]string, len(messages))
-	for i, m := range messages {
-		ciphertexts[i] = m.SegmentsEncrypted
-	}
-
-	// 批量并行解密
-	plaintexts := encryptor.BatchDecrypt(ciphertexts, workerCount)
-
-	// 解析结果
-	for i, m := range messages {
-		if m.decrypted {
-			continue
-		}
-		if m.SegmentsEncrypted == "" {
-			m.decrypted = true
-			continue
-		}
-
-		plaintext := plaintexts[i]
-		if plaintext == nil {
-			// 解密失败，尝试直接解析（兼容旧数据）
-			if err := json.Unmarshal([]byte(m.SegmentsEncrypted), &m.Segments); err != nil {
-				continue // 忽略单条错误
-			}
-		} else {
-			if err := json.Unmarshal(plaintext, &m.Segments); err != nil {
-				continue // 忽略单条错误
-			}
-		}
-		m.decrypted = true
-	}
-
-	return nil
-}
 
 // BatchDecryptMessagesParallel 使用 worker pool 并行解密
 // 这是一个更高效的版本，适用于大量消息