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/handler.go

@@ -19,6 +19,7 @@ var HandlerSet = wire.NewSet(
 	handler.NewPushHandler,
 	handler.NewStickerHandler,
 	handler.NewVoteHandler,
+	handler.NewChannelHandler,
 	handler.NewRoleHandler,
 	handler.NewAdminUserHandler,
 	handler.NewAdminPostHandler,