refactor: introduce Wire dependency injection and interface-based architecture

- Add Google Wire for compile-time dependency injection
- Replace concrete service types with interfaces across handlers
- Remove global state (DB, cache) in favor of constructor injection
- Split monolithic files into focused modules:
  - config: separate files for each config domain
  - dto: converters split by domain (user, post, message, group)
  - cache: separate metrics.go and redis_cache.go
- Introduce unified apperrors package with string-based error codes
- Add transaction support with context-aware repository methods
- Upgrade golang.org/x/crypto from 0.17.0 to 0.26.0

internal/dto/message_converter.go

@@ -0,0 +1,178 @@
+package dto
+
+import (
+	"carrot_bbs/internal/model"
+)
+
+// ==================== Message 转换 ====================
+
+// ConvertMessageToResponse 将Message转换为MessageResponse
+func ConvertMessageToResponse(message *model.Message) *MessageResponse {
+	if message == nil {
+		return nil
+	}
+
+	// 直接使用 segments，不需要解析
+	segments := make(model.MessageSegments, len(message.Segments))
+	for i, seg := range message.Segments {
+		segments[i] = model.MessageSegment{
+			Type: seg.Type,
+			Data: seg.Data,
+		}
+	}
+
+	return &MessageResponse{
+		ID:             message.ID,
+		ConversationID: message.ConversationID,
+		SenderID:       message.SenderID,
+		Seq:            message.Seq,
+		Segments:       segments,
+		ReplyToID:      message.ReplyToID,
+		Status:         string(message.Status),
+		Category:       string(message.Category),
+		CreatedAt:      FormatTime(message.CreatedAt),
+	}
+}
+
+// ConvertConversationToResponse 将Conversation转换为ConversationResponse
+// participants: 会话参与者列表（用户信息）
+// unreadCount: 当前用户的未读消息数
+// lastMessage: 最后一条消息
+func ConvertConversationToResponse(conv *model.Conversation, participants []*model.User, unreadCount int, lastMessage *model.Message, isPinned bool) *ConversationResponse {
+	if conv == nil {
+		return nil
+	}
+
+	var participantResponses []*UserResponse
+	for _, p := range participants {
+		participantResponses = append(participantResponses, ConvertUserToResponse(p))
+	}
+
+	// 转换群组信息
+	var groupResponse *GroupResponse
+	if conv.Group != nil {
+		groupResponse = GroupToResponse(conv.Group)
+	}
+
+	return &ConversationResponse{
+		ID:            conv.ID,
+		Type:          string(conv.Type),
+		IsPinned:      isPinned,
+		Group:         groupResponse,
+		LastSeq:       conv.LastSeq,
+		LastMessage:   ConvertMessageToResponse(lastMessage),
+		LastMessageAt: FormatTimePointer(conv.LastMsgTime),
+		UnreadCount:   unreadCount,
+		Participants:  participantResponses,
+		CreatedAt:     FormatTime(conv.CreatedAt),
+		UpdatedAt:     FormatTime(conv.UpdatedAt),
+	}
+}
+
+// ConvertConversationToDetailResponse 将Conversation转换为ConversationDetailResponse
+func ConvertConversationToDetailResponse(conv *model.Conversation, participants []*model.User, unreadCount int64, lastMessage *model.Message, myLastReadSeq int64, otherLastReadSeq int64, isPinned bool) *ConversationDetailResponse {
+	if conv == nil {
+		return nil
+	}
+
+	var participantResponses []*UserResponse
+	for _, p := range participants {
+		participantResponses = append(participantResponses, ConvertUserToResponse(p))
+	}
+
+	return &ConversationDetailResponse{
+		ID:               conv.ID,
+		Type:             string(conv.Type),
+		IsPinned:         isPinned,
+		LastSeq:          conv.LastSeq,
+		LastMessage:      ConvertMessageToResponse(lastMessage),
+		LastMessageAt:    FormatTimePointer(conv.LastMsgTime),
+		UnreadCount:      unreadCount,
+		Participants:     participantResponses,
+		MyLastReadSeq:    myLastReadSeq,
+		OtherLastReadSeq: otherLastReadSeq,
+		CreatedAt:        FormatTime(conv.CreatedAt),
+		UpdatedAt:        FormatTime(conv.UpdatedAt),
+	}
+}
+
+// ConvertMessagesToResponse 将Message列表转换为响应列表
+func ConvertMessagesToResponse(messages []*model.Message) []*MessageResponse {
+	result := make([]*MessageResponse, 0, len(messages))
+	for _, msg := range messages {
+		result = append(result, ConvertMessageToResponse(msg))
+	}
+	return result
+}
+
+// ConvertConversationsToResponse 将Conversation列表转换为响应列表
+func ConvertConversationsToResponse(convs []*model.Conversation) []*ConversationResponse {
+	result := make([]*ConversationResponse, 0, len(convs))
+	for _, conv := range convs {
+		result = append(result, ConvertConversationToResponse(conv, nil, 0, nil, false))
+	}
+	return result
+}
+
+// ==================== PushRecord 转换 ====================
+
+// PushRecordToResponse 将PushRecord转换为PushRecordResponse
+func PushRecordToResponse(record *model.PushRecord) *PushRecordResponse {
+	if record == nil {
+		return nil
+	}
+	resp := &PushRecordResponse{
+		ID:          record.ID,
+		MessageID:   record.MessageID,
+		PushChannel: string(record.PushChannel),
+		PushStatus:  string(record.PushStatus),
+		RetryCount:  record.RetryCount,
+		CreatedAt:   record.CreatedAt,
+	}
+	if record.PushedAt != nil {
+		resp.PushedAt = *record.PushedAt
+	}
+	if record.DeliveredAt != nil {
+		resp.DeliveredAt = *record.DeliveredAt
+	}
+	return resp
+}
+
+// PushRecordsToResponse 将PushRecord列表转换为响应列表
+func PushRecordsToResponse(records []*model.PushRecord) []*PushRecordResponse {
+	result := make([]*PushRecordResponse, 0, len(records))
+	for _, record := range records {
+		result = append(result, PushRecordToResponse(record))
+	}
+	return result
+}
+
+// ==================== DeviceToken 转换 ====================
+
+// DeviceTokenToResponse 将DeviceToken转换为DeviceTokenResponse
+func DeviceTokenToResponse(token *model.DeviceToken) *DeviceTokenResponse {
+	if token == nil {
+		return nil
+	}
+	resp := &DeviceTokenResponse{
+		ID:         token.ID,
+		DeviceID:   token.DeviceID,
+		DeviceType: string(token.DeviceType),
+		IsActive:   token.IsActive,
+		DeviceName: token.DeviceName,
+		CreatedAt:  token.CreatedAt,
+	}
+	if token.LastUsedAt != nil {
+		resp.LastUsedAt = *token.LastUsedAt
+	}
+	return resp
+}
+
+// DeviceTokensToResponse 将DeviceToken列表转换为响应列表
+func DeviceTokensToResponse(tokens []*model.DeviceToken) []*DeviceTokenResponse {
+	result := make([]*DeviceTokenResponse, 0, len(tokens))
+	for _, token := range tokens {
+		result = append(result, DeviceTokenToResponse(token))
+	}
+	return result
+}