feat(post): implement share recording functionality

- Added RecordShare method in PostHandler to handle sharing posts and increment share count.
- Introduced IncrementShares method in PostRepository to update shares_count for published posts.
- Updated PostService to include RecordShare, ensuring cache invalidation for post details and lists.
- Integrated new share route in the router for handling share requests.

internal/handler/post_handler.go

@@ -6,6 +6,7 @@ import (
 	"strconv"
 
 	"github.com/gin-gonic/gin"
+	"gorm.io/gorm"
 
 	"carrot_bbs/internal/dto"
 	"carrot_bbs/internal/model"
@@ -145,6 +146,41 @@ func (h *PostHandler) RecordView(c *gin.Context) {
 	response.Success(c, gin.H{"success": true})
 }
 
+// RecordShare 记录帖子分享（shares_count +1，仅已发布）
+// 支持可选 JSON：{"channel":"wechat"|"qq"|"copy_link"|"system"|...}，用于后续统计
+func (h *PostHandler) RecordShare(c *gin.Context) {
+	id := c.Param("id")
+	_ = c.GetString("user_id") // 预留：登录用户维度统计
+
+	type shareBody struct {
+		Channel string `json:"channel"`
+	}
+	var body shareBody
+	if c.Request.ContentLength > 0 {
+		if err := c.ShouldBindJSON(&body); err != nil {
+			response.BadRequest(c, "invalid json body")
+			return
+		}
+	}
+
+	sharesCount, err := h.postService.RecordShare(c.Request.Context(), id, c.GetString("user_id"))
+	if err != nil {
+		if errors.Is(err, gorm.ErrRecordNotFound) {
+			response.NotFound(c, "post not found")
+			return
+		}
+		fmt.Printf("[ERROR] RecordShare post %s: %v\n", id, err)
+		response.InternalServerError(c, "failed to record share")
+		return
+	}
+
+	data := gin.H{"success": true, "shares_count": sharesCount}
+	if body.Channel != "" {
+		data["channel"] = body.Channel
+	}
+	response.Success(c, data)
+}
+
 // List 获取帖子列表（支持游标分页和偏移分页）
 func (h *PostHandler) List(c *gin.Context) {
 	// 检查是否使用游标分页