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/service/channel_service.go

@@ -0,0 +1,65 @@
+package service
+
+import (
+	"carrot_bbs/internal/model"
+	"carrot_bbs/internal/repository"
+)
+
+type ChannelService interface {
+	ListActive() ([]*model.Channel, error)
+	ListAll() ([]*model.Channel, error)
+	Create(name, slug, description string, sortOrder int, isActive bool) (*model.Channel, error)
+	Update(id, name, slug, description string, sortOrder int, isActive bool) (*model.Channel, error)
+	Delete(id string) error
+}
+
+type channelServiceImpl struct {
+	channelRepo *repository.ChannelRepository
+}
+
+func NewChannelService(channelRepo *repository.ChannelRepository) ChannelService {
+	return &channelServiceImpl{channelRepo: channelRepo}
+}
+
+func (s *channelServiceImpl) ListActive() ([]*model.Channel, error) {
+	return s.channelRepo.ListActive()
+}
+
+func (s *channelServiceImpl) ListAll() ([]*model.Channel, error) {
+	return s.channelRepo.ListAll()
+}
+
+func (s *channelServiceImpl) Create(name, slug, description string, sortOrder int, isActive bool) (*model.Channel, error) {
+	channel := &model.Channel{
+		Name:        name,
+		Slug:        slug,
+		Description: description,
+		SortOrder:   sortOrder,
+		IsActive:    isActive,
+	}
+	if err := s.channelRepo.Create(channel); err != nil {
+		return nil, err
+	}
+	return channel, nil
+}
+
+func (s *channelServiceImpl) Update(id, name, slug, description string, sortOrder int, isActive bool) (*model.Channel, error) {
+	channel, err := s.channelRepo.GetByID(id)
+	if err != nil {
+		return nil, err
+	}
+	channel.Name = name
+	channel.Slug = slug
+	channel.Description = description
+	channel.SortOrder = sortOrder
+	channel.IsActive = isActive
+	if err := s.channelRepo.Update(channel); err != nil {
+		return nil, err
+	}
+	return channel, nil
+}
+
+func (s *channelServiceImpl) Delete(id string) error {
+	return s.channelRepo.Delete(id)
+}
+