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

@@ -143,9 +143,12 @@ class GarageScreenState extends State<GarageScreen> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      body: CustomScrollView(
-        controller: _scrollController,
-        slivers: [
+      body: RefreshIndicator(
+        onRefresh: () => _loadCars(reset: true),
+        child: CustomScrollView(
+          controller: _scrollController,
+          physics: const AlwaysScrollableScrollPhysics(),
+          slivers: [
           SliverAppBar(
             expandedHeight: 140,
             pinned: true,
@@ -297,7 +300,8 @@ class GarageScreenState extends State<GarageScreen> {
                 child: Center(child: CircularProgressIndicator(strokeWidth: 2)),
               ),
             ),
-        ],
+          ],
+        ),
       ),
       bottomNavigationBar: _selectionMode
           ? SafeArea(