refactor(cache): remove deprecated unread count methods and keys

Clean up the codebase by removing unused and deprecated unread count
functionality in `ConversationCache` and associated Redis key
generators. This follows the transition to sequence-based unread
calculation.

- Remove `IncrementUnread`, `ClearUnread`, `GetUnreadCountFromHash`,
  `GetAllUnreadCounts`, and `GetTotalUnread` from `ConversationCache`.
- Remove `PrefixUnreadHash` and `PrefixUnreadTotal` constants and
  `UnreadHashKey`/`UnreadTotalKey` helper functions.
- Remove unused `isValidContentType` helper in `MessageHandler`.

internal/cache/conversation_cache.go

@@ -692,36 +692,6 @@ func (c *ConversationCache) ComputeAllUnreadCount(ctx context.Context, userID st
 	return total, nil
 }
 
-// IncrementUnread 递增用户在某会话的未读数（已废弃：改用 seq 算术计算）
-// Deprecated: Unread count is now computed via arithmetic (maxSeq - readSeq).
-func (c *ConversationCache) IncrementUnread(ctx context.Context, userID, convID string) error {
-	return nil
-}
-
-// ClearUnread 清零用户在某会话的未读数（已废弃：改用 seq 算术计算）
-// Deprecated: No longer needed. Unread is computed from seq arithmetic.
-func (c *ConversationCache) ClearUnread(ctx context.Context, userID, convID string) error {
-	return nil
-}
-
-// GetUnreadCountFromHash 从 Redis Hash 获取单个会话未读数（已废弃）
-// Deprecated: Use ComputeUnreadCount instead.
-func (c *ConversationCache) GetUnreadCountFromHash(ctx context.Context, userID, convID string) (int64, error) {
-	return 0, ErrKeyNotFound
-}
-
-// GetAllUnreadCounts 从 Redis Hash 获取用户所有会话的未读数（已废弃）
-// Deprecated: Use ComputeAllUnreadCount instead.
-func (c *ConversationCache) GetAllUnreadCounts(ctx context.Context, userID string) (map[string]int64, error) {
-	return nil, ErrKeyNotFound
-}
-
-// GetTotalUnread 从 Redis 获取用户总未读数（已废弃）
-// Deprecated: Use ComputeAllUnreadCount instead.
-func (c *ConversationCache) GetTotalUnread(ctx context.Context, userID string) (int64, error) {
-	return 0, ErrKeyNotFound
-}
-
 // GetNextSeq 获取会话的下一个 seq 值（原子递增）
 // 使用 Redis INCR 实现，首次调用时从 DB 初始化并补齐差值
 func (c *ConversationCache) GetNextSeq(ctx context.Context, convID string) (int64, error) {

internal/cache/keys.go

@@ -26,8 +26,6 @@ const (
 	PrefixUnreadSystem       = "unread:system"
 	PrefixUnreadConversation = "unread:conversation"
 	PrefixUnreadDetail       = "unread:detail"
-	PrefixUnreadHash         = "unread:hash"
-	PrefixUnreadTotal        = "unread:total"
 		
 	// 已读位置相关（OpenIM 风格：缓存 hasReadSeq，用于 O(1) 未读数计算）
 	PrefixUserReadSeq = "user_read_seq"
@@ -123,16 +121,6 @@ func UnreadDetailKey(userID, conversationID string) string {
 	return fmt.Sprintf("%s:%s:%s", PrefixUnreadDetail, userID, conversationID)
 }
 
-// UnreadHashKey 生成用户未读数 Hash 缓存键
-func UnreadHashKey(userID string) string {
-	return fmt.Sprintf("%s:%s", PrefixUnreadHash, userID)
-}
-
-// UnreadTotalKey 生成用户总未读数计数器键
-func UnreadTotalKey(userID string) string {
-	return fmt.Sprintf("%s:%s", PrefixUnreadTotal, userID)
-}
-
 // UserInfoKey 生成用户信息缓存键
 func UserInfoKey(userID string) string {
 	return fmt.Sprintf("%s:%s", PrefixUserInfo, userID)

internal/handler/message_handler.go

@@ -653,16 +653,6 @@ func (h *MessageHandler) DeleteMessage(c *gin.Context) {
 	response.SuccessWithMessage(c, "message deleted", nil)
 }
 
-// 辅助函数：验证内容类型
-func isValidContentType(contentType model.ContentType) bool {
-	switch contentType {
-	case model.ContentTypeText, model.ContentTypeImage, model.ContentTypeVideo, model.ContentTypeAudio, model.ContentTypeFile:
-		return true
-	default:
-		return false
-	}
-}
-
 // 辅助函数：获取会话参与者信息
 func (h *MessageHandler) getConversationParticipants(ctx context.Context, conversationID string, currentUserID string) ([]*model.User, error) {
 	// 从repository获取参与者列表