feat: add sort and order params to admin market list

Supports sorting by name, city, date, created, status with asc/desc order.

backend/internal/domain/market/dto.go

@@ -153,6 +153,8 @@ func ToDetail(m Market) MarketDetail {
 type AdminSearchParams struct {
 	Status  string `form:"status"`
 	Query   string `form:"q"`
+	Sort    string `form:"sort"`  // name, city, date, created, status
+	Order   string `form:"order"` // asc, desc
 	Page    int    `form:"page"`
 	PerPage int    `form:"per_page"`
 }

backend/internal/domain/market/repository.go

@@ -474,13 +474,31 @@ func (r *pgRepository) AdminSearch(ctx context.Context, params AdminSearchParams
 	offsetArg := nextArg()
 	args = append(args, params.PerPage, params.Offset())
 
+	orderCol := "m.created_at"
+	switch params.Sort {
+	case "name":
+		orderCol = "m.name"
+	case "city":
+		orderCol = "m.city"
+	case "date":
+		orderCol = "m.start_date"
+	case "created":
+		orderCol = "m.created_at"
+	case "status":
+		orderCol = "m.status"
+	}
+	orderDir := "DESC"
+	if params.Order == "asc" {
+		orderDir = "ASC"
+	}
+
 	dataQuery := fmt.Sprintf(`
 		SELECT %s
 		FROM markets m
 		%s
-		ORDER BY m.created_at DESC
+		ORDER BY %s %s
 		LIMIT %s OFFSET %s
-	`, selectFullColumns, where, limitArg, offsetArg)
+	`, selectFullColumns, where, orderCol, orderDir, limitArg, offsetArg)
 
 	rows, err := r.db.Query(ctx, dataQuery, args...)
 	if err != nil {