提交1: 数据层改造 - 发布群与企业微信群二维码

- 新增数据库迁移 000008: chat_conversations 增加 listing_id, 新建 chat_qrcode_pool 表
- 更新 GORM 模型: ChatConversation 新增 ListingID 字段, 新增 ChatQrCode 模型
- 实现二维码池管理后端 API: 创建/列表/统计/更新/删除
- 新增管理后台路由: /api/admin/chats/qrcodes
- 新增系统配置: chat.listing_group_welcome, chat.qrcode_low_stock_threshold
- 更新优化方案文档: 废弃双群方案, 采用单群方案

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/internal/modules/chat/handler_qrcode.go

@@ -0,0 +1,111 @@
+package chat
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/gin-gonic/gin"
+)
+
+// CreateQrCodeHandler 创建二维码
+func (h *Handler) CreateQrCodeHandler(c *gin.Context) {
+	var req CreateQrCodeRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	adminID := c.GetUint64("admin_id")
+	qrcode, err := h.service.repo.CreateQrCode(c.Request.Context(), adminID, req)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{"data": qrcode})
+}
+
+// ListQrCodesHandler 列表查询二维码
+func (h *Handler) ListQrCodesHandler(c *gin.Context) {
+	var req QrCodeListRequest
+	if err := c.ShouldBindQuery(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	qrcodes, total, err := h.service.repo.ListQrCodes(c.Request.Context(), req)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{
+		"data": qrcodes,
+		"pagination": gin.H{
+			"total": total,
+			"page":  req.Page,
+			"limit": req.Limit,
+		},
+	})
+}
+
+// GetQrCodeStatsHandler 获取二维码统计
+func (h *Handler) GetQrCodeStatsHandler(c *gin.Context) {
+	stats, err := h.service.repo.GetQrCodeStats(c.Request.Context())
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{"data": stats})
+}
+
+// UpdateQrCodeHandler 更新二维码
+func (h *Handler) UpdateQrCodeHandler(c *gin.Context) {
+	id, err := strconv.ParseUint(c.Param("id"), 10, 64)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "无效的ID"})
+		return
+	}
+
+	var req UpdateQrCodeRequest
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		return
+	}
+
+	if err := h.service.repo.UpdateQrCode(c.Request.Context(), id, req); err != nil {
+		if err == ErrQrCodeNotFound {
+			c.JSON(http.StatusNotFound, gin.H{"error": "二维码不存在"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{"message": "更新成功"})
+}
+
+// DeleteQrCodeHandler 删除二维码
+func (h *Handler) DeleteQrCodeHandler(c *gin.Context) {
+	id, err := strconv.ParseUint(c.Param("id"), 10, 64)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "无效的ID"})
+		return
+	}
+
+	if err := h.service.repo.DeleteQrCode(c.Request.Context(), id); err != nil {
+		if err == ErrQrCodeNotFound {
+			c.JSON(http.StatusNotFound, gin.H{"error": "二维码不存在"})
+			return
+		}
+		if err == ErrQrCodeCannotDelete {
+			c.JSON(http.StatusBadRequest, gin.H{"error": "已使用的二维码不能删除"})
+			return
+		}
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{"message": "删除成功"})
+}