feat(brand): add brand sort order and drag-to-reorder

Add a sort_order column to brands with a migration, expose a
PUT /api/tenant/brands/order reorder endpoint, and wire the
admin-web BrandsView with drag-and-drop reordering plus i18n.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/tenant/transport/router_test.go

@@ -43,6 +43,7 @@ func TestProtectedRoutes_RequireAuth(t *testing.T) {
 		{http.MethodGet, "/api/tenant/articles"},
 		{http.MethodGet, "/api/tenant/brands"},
 		{http.MethodGet, "/api/tenant/brands/library-summary"},
+		{http.MethodPut, "/api/tenant/brands/order"},
 		{http.MethodGet, "/api/tenant/monitoring/brands/:brand_id/questions/:question_id/detail"},
 		{http.MethodGet, "/api/tenant/monitoring/marked-articles"},
 		{http.MethodPost, "/api/tenant/monitoring/marked-articles"},