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/handler/channel_handler.go

@@ -0,0 +1,123 @@
+package handler
+
+import (
+	"carrot_bbs/internal/model"
+	"carrot_bbs/internal/pkg/response"
+	"carrot_bbs/internal/service"
+
+	"github.com/gin-gonic/gin"
+)
+
+type ChannelHandler struct {
+	channelService service.ChannelService
+}
+
+func NewChannelHandler(channelService service.ChannelService) *ChannelHandler {
+	return &ChannelHandler{channelService: channelService}
+}
+
+type channelResponse struct {
+	ID          string `json:"id"`
+	Name        string `json:"name"`
+	Slug        string `json:"slug"`
+	Description string `json:"description,omitempty"`
+	SortOrder   int    `json:"sort_order"`
+	IsActive    bool   `json:"is_active"`
+}
+
+func toChannelResponse(c *model.Channel) *channelResponse {
+	if c == nil {
+		return nil
+	}
+	return &channelResponse{
+		ID:          c.ID,
+		Name:        c.Name,
+		Slug:        c.Slug,
+		Description: c.Description,
+		SortOrder:   c.SortOrder,
+		IsActive:    c.IsActive,
+	}
+}
+
+// ListPublic 公开频道列表（仅启用）
+func (h *ChannelHandler) ListPublic(c *gin.Context) {
+	items, err := h.channelService.ListActive()
+	if err != nil {
+		response.InternalServerError(c, "failed to get channels")
+		return
+	}
+	result := make([]*channelResponse, 0, len(items))
+	for _, item := range items {
+		result = append(result, toChannelResponse(item))
+	}
+	response.Success(c, gin.H{"list": result})
+}
+
+// AdminList 管理端频道列表（全部）
+func (h *ChannelHandler) AdminList(c *gin.Context) {
+	items, err := h.channelService.ListAll()
+	if err != nil {
+		response.InternalServerError(c, "failed to get channels")
+		return
+	}
+	result := make([]*channelResponse, 0, len(items))
+	for _, item := range items {
+		result = append(result, toChannelResponse(item))
+	}
+	response.Success(c, gin.H{"list": result})
+}
+
+type adminChannelUpsertRequest struct {
+	Name        string `json:"name" binding:"required,max=100"`
+	Slug        string `json:"slug" binding:"required,max=100"`
+	Description string `json:"description" binding:"max=255"`
+	SortOrder   int    `json:"sort_order"`
+	IsActive    *bool  `json:"is_active"`
+}
+
+func (h *ChannelHandler) AdminCreate(c *gin.Context) {
+	var req adminChannelUpsertRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, err.Error())
+		return
+	}
+	isActive := true
+	if req.IsActive != nil {
+		isActive = *req.IsActive
+	}
+	item, err := h.channelService.Create(req.Name, req.Slug, req.Description, req.SortOrder, isActive)
+	if err != nil {
+		response.InternalServerError(c, "failed to create channel")
+		return
+	}
+	response.Success(c, toChannelResponse(item))
+}
+
+func (h *ChannelHandler) AdminUpdate(c *gin.Context) {
+	id := c.Param("id")
+	var req adminChannelUpsertRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		response.BadRequest(c, err.Error())
+		return
+	}
+	isActive := true
+	if req.IsActive != nil {
+		isActive = *req.IsActive
+	}
+	item, err := h.channelService.Update(id, req.Name, req.Slug, req.Description, req.SortOrder, isActive)
+	if err != nil {
+		response.InternalServerError(c, "failed to update channel")
+		return
+	}
+	response.Success(c, toChannelResponse(item))
+}
+
+func (h *ChannelHandler) AdminDelete(c *gin.Context) {
+	id := c.Param("id")
+	if err := h.channelService.Delete(id); err != nil {
+		response.InternalServerError(c, "failed to delete channel")
+		return
+	}
+	response.Success(c, gin.H{"success": true})
+}
+