feat(garage): add pull-to-refresh for collection gallery sync

- Wrap garage grid in RefreshIndicator
- Trigger full paged reload on pull gesture
- Use always-scrollable physics so refresh works even on short lists
- Improve manual sync flow for shared collection updates

lib/screens/garage_screen.dart

@@ -143,8 +143,11 @@ class GarageScreenState extends State<GarageScreen> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      body: CustomScrollView(
+      body: RefreshIndicator(
+        onRefresh: () => _loadCars(reset: true),
+        child: CustomScrollView(
           controller: _scrollController,
+          physics: const AlwaysScrollableScrollPhysics(),
           slivers: [
           SliverAppBar(
             expandedHeight: 140,
@@ -299,6 +302,7 @@ class GarageScreenState extends State<GarageScreen> {
             ),
           ],
         ),
+      ),
       bottomNavigationBar: _selectionMode
           ? SafeArea(
               top: false,