feat(garage): add single-car move action from detail sheet

- Add Move action to car detail controls (Move / Edit / Remove)
- Introduce target collection picker dialog for single-entry move
- Reuse existing collection membership logic and refresh grid after move
- Keep bulk multi-select move workflow unchanged

lib/screens/garage_screen.dart

@@ -601,6 +601,14 @@ class GarageScreenState extends State<GarageScreen> {
             // Edit & Delete buttons
             Row(
               children: [
+                Expanded(
+                  child: OutlinedButton.icon(
+                    onPressed: () => _moveSingleCar(car, context),
+                    icon: const Icon(Icons.drive_file_move_outline, size: 18),
+                    label: const Text('Move'),
+                  ),
+                ),
+                const SizedBox(width: 8),
                 Expanded(
                   child: ElevatedButton.icon(
                     onPressed: () => _editCar(car, context),
@@ -608,7 +616,7 @@ class GarageScreenState extends State<GarageScreen> {
                     label: const Text('Edit Details'),
                   ),
                 ),
-                const SizedBox(width: 12),
+                const SizedBox(width: 8),
                 Expanded(
                   child: OutlinedButton.icon(
                     onPressed: () => _deleteCar(car, context),
@@ -714,6 +722,80 @@ class GarageScreenState extends State<GarageScreen> {
     }
   }
 
+  Future<String?> _pickTargetCollection() async {
+    final collections = await CollectionService.getMyCollections();
+    if (!mounted) return null;
+
+    final candidates = collections
+        .where((c) => c.id != widget.collectionId)
+        .toList(growable: false);
+
+    if (candidates.isEmpty) {
+      showGlobalSnackBar('No other collection available.', isError: true);
+      return null;
+    }
+
+    String? targetId;
+    final confirmed = await showDialog<bool>(
+      context: context,
+      builder: (_) => StatefulBuilder(
+        builder: (context, setSheetState) => AlertDialog(
+          title: const Text('Move Car'),
+          content: DropdownButtonFormField<String>(
+            initialValue: targetId,
+            decoration: const InputDecoration(
+              labelText: 'Target collection',
+            ),
+            items: candidates
+                .map(
+                  (c) => DropdownMenuItem<String>(
+                    value: c.id,
+                    child: Text(c.name),
+                  ),
+                )
+                .toList(),
+            onChanged: (value) => setSheetState(() => targetId = value),
+          ),
+          actions: [
+            TextButton(
+              onPressed: () => Navigator.pop(context, false),
+              child: const Text('Cancel'),
+            ),
+            ElevatedButton(
+              onPressed: targetId == null
+                  ? null
+                  : () => Navigator.pop(context, true),
+              child: const Text('Move'),
+            ),
+          ],
+        ),
+      ),
+    );
+
+    if (confirmed != true || targetId == null) return null;
+    return targetId;
+  }
+
+  Future<void> _moveSingleCar(
+      Map<String, dynamic> car, BuildContext sheetContext) async {
+    try {
+      final targetId = await _pickTargetCollection();
+      if (targetId == null) return;
+
+      await supabase
+          .from('hotwheels')
+          .update({'collection_id': targetId})
+          .eq('id', car['id']);
+
+      if (!mounted) return;
+      if (sheetContext.mounted) Navigator.pop(sheetContext);
+      showGlobalSnackBar('${car['hw_id']} moved to another collection.');
+      await _loadCars(reset: true);
+    } catch (e) {
+      showGlobalSnackBar('Failed to move car: $e', isError: true);
+    }
+  }
+
   Future<void> _deleteCar(
       Map<String, dynamic> car, BuildContext sheetContext) async {
     if (!sheetContext.mounted) return;