fix(backend): JWT config mapstructure tag 修复 + 模型从 hotel 重构为 shop

- 修复 JWTConfig 缺少 mapstructure tag 导致 access_expire_min 解析为 0，
  token 签发即过期，所有 API 请求返回 401
- 全部 config struct 补齐 mapstructure tag（secret/dsn/hmac_secret 等）
- 模型层从 hotel/HotelID 统一重命名为 shop/ShopID
- 删除旧 migrations（001-004），新增 001_init 综合迁移文件
- 更新 schema.sql、testutil、handler/service/model 相关引用

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/handler/auth.go

@@ -18,16 +18,16 @@ func NewAuthHandler(svc *service.AuthService) *AuthHandler {
 // Login POST /api/v1/auth/login
 func (h *AuthHandler) Login(c *gin.Context) {
 	var req struct {
-		HotelCode string `json:"hotel_code" binding:"required"`
-		Username  string `json:"username" binding:"required"`
-		Password  string `json:"password" binding:"required"`
+		ShopCode string `json:"shop_code" binding:"required"`
+		Username string `json:"username" binding:"required"`
+		Password string `json:"password" binding:"required"`
 	}
 	if err := c.ShouldBindJSON(&req); err != nil {
 		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
 		return
 	}
 
-	pair, user, err := h.svc.Login(req.HotelCode, req.Username, req.Password)
+	pair, user, err := h.svc.Login(req.ShopCode, req.Username, req.Password)
 	if err != nil {
 		c.JSON(http.StatusUnauthorized, gin.H{"error": err.Error()})
 		return
@@ -38,6 +38,7 @@ func (h *AuthHandler) Login(c *gin.Context) {
 			"access_token":  pair.AccessToken,
 			"refresh_token": pair.RefreshToken,
 			"expires_in":    pair.ExpiresIn,
+			"shop_id":       pair.ShopID,
 			"user": gin.H{
 				"id":        user.ID,
 				"username":  user.Username,