feat(channel): integrate channel functionality into post management

- Added Channel support in Post model, including ChannelID field in PostRequest and PostResponse DTOs.
- Updated PostService and PostRepository to handle channel-specific logic for creating and listing posts.
- Introduced ChannelRepository and ChannelService, along with corresponding handlers for managing channels.
- Enhanced router to include routes for channel management and public channel listing.
- Seeded default channels in the database during initialization.

internal/wire/service.go

@@ -39,6 +39,7 @@ var ServiceSet = wire.NewSet(
 	ProvideUserService,
 	ProvideStickerService,
 	ProvideVoteService,
+	ProvideChannelService,
 	ProvideChatService,
 	ProvideScheduleService,
 	ProvideScheduleSyncService,
@@ -172,6 +173,10 @@ func ProvideVoteService(
 	return service.NewVoteService(voteRepo, postRepo, cache, postAIService, systemMessageService)
 }
 
+func ProvideChannelService(channelRepo *repository.ChannelRepository) service.ChannelService {
+	return service.NewChannelService(channelRepo)
+}
+
 // ProvideChatService 提供聊天服务
 // Note: sensitiveService 传 nil，与 main.go 保持一致
 func ProvideChatService(