feat(admin): sortable product list column headers

Click a column header (名称/品牌/条码/品类/状态/质量分) to sort asc, click
again for desc, and a third time to clear back to the default
most-recently-updated order. Sort key/direction are whitelisted server-side.

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

api/internal/adminhandler/handler.go

@@ -164,8 +164,10 @@ func (h *Handler) Me(w http.ResponseWriter, r *http.Request) {
 // ListProducts returns a paginated product list.
 func (h *Handler) ListProducts(w http.ResponseWriter, r *http.Request) {
 	q := r.URL.Query().Get("q")
+	sort := r.URL.Query().Get("sort")
+	order := r.URL.Query().Get("order")
 	page, size := pageParams(r)
-	items, total, err := h.store.ListProducts(r.Context(), q, size, (page-1)*size)
+	items, total, err := h.store.ListProducts(r.Context(), q, sort, order, size, (page-1)*size)
 	if h.handleErr(w, err) {
 		return
 	}