perf: avoid redundant tab refresh traffic

lib/screens/collections_screen.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import '../main.dart';
 import '../services/collection_service.dart';
+import '../services/main_collection_sync.dart';
 import '../theme/app_colors.dart';
 import 'garage_screen.dart';
 import 'manage_collection_screen.dart';
@@ -172,6 +173,7 @@ class CollectionsScreenState extends State<CollectionsScreen> {
     await prefs.setString(_activeCollectionPrefKey, collectionId);
     if (!mounted) return;
     setState(() => _activeCollectionId = collectionId);
+    MainCollectionSync.notifyChanged();
     showGlobalSnackBar('Main collection set for scanning.');
   }
 

lib/screens/home_shell.dart

@@ -24,12 +24,6 @@ class _HomeShellState extends State<HomeShell> {
 
   void _onTabSelected(int i) {
     setState(() => _currentIndex = i);
-
-    if (i == 0) {
-      _collectionsKey.currentState?.refresh();
-    } else if (i == 1) {
-      _scanKey.currentState?.refresh();
-    }
   }
 
   @override

lib/screens/scan_tab.dart

@@ -3,6 +3,7 @@ import 'package:shared_preferences/shared_preferences.dart';
 import '../main.dart';
 import '../scanner_screen.dart';
 import '../services/collection_service.dart';
+import '../services/main_collection_sync.dart';
 import '../theme/app_colors.dart';
 
 class ScanTab extends StatefulWidget {
@@ -26,11 +27,23 @@ class ScanTabState extends State<ScanTab> {
   @override
   void initState() {
     super.initState();
+    MainCollectionSync.changeToken.addListener(_handleMainCollectionChanged);
     _loadCollections();
   }
 
+  @override
+  void dispose() {
+    MainCollectionSync.changeToken.removeListener(_handleMainCollectionChanged);
+    super.dispose();
+  }
+
   void refresh() => _loadCollections();
 
+  void _handleMainCollectionChanged() {
+    if (!mounted) return;
+    _loadCollections();
+  }
+
   Future<void> _loadCollections() async {
     try {
       final list = await CollectionService.getMyCollections();

lib/services/main_collection_sync.dart

@@ -0,0 +1,11 @@
+import 'package:flutter/foundation.dart';
+
+class MainCollectionSync {
+  MainCollectionSync._();
+
+  static final ValueNotifier<int> changeToken = ValueNotifier<int>(0);
+
+  static void notifyChanged() {
+    changeToken.value = changeToken.value + 1;
+  }
+}