feat: Implement change detection and conditional enabling of save/cancel buttons for profile and notification settings.

lib/features/profile/presentation/widgets/notifications_tab.dart

@@ -26,6 +26,17 @@ class _NotificationsTabState extends ConsumerState<NotificationsTab> {
   Map<String, Map<String, bool>> _originalPrefs = {};
   String _originalFrequency = 'instant';
 
+  bool get _hasNotificationChanges {
+    if (_digestFrequency != _originalFrequency) return true;
+    for (final key in _notificationPrefs.keys) {
+      final current = _notificationPrefs[key];
+      final original = _originalPrefs[key];
+      if (current == null || original == null) return true;
+      if (current['email'] != original['email'] || current['inApp'] != original['inApp']) return true;
+    }
+    return false;
+  }
+
   @override
   void initState() {
     super.initState();
@@ -154,6 +165,7 @@ class _NotificationsTabState extends ConsumerState<NotificationsTab> {
         ProfileActionButtons(
           onSave: _saveNotificationSettings,
           onCancel: () {
+            if (!_hasNotificationChanges) return;
             setState(() {
               for (final key in _originalPrefs.keys) {
                 _notificationPrefs[key] = Map<String, bool>.from(_originalPrefs[key]!);
@@ -162,6 +174,7 @@ class _NotificationsTabState extends ConsumerState<NotificationsTab> {
             });
           },
           isSaving: _isSavingNotifications,
+          hasChanges: _hasNotificationChanges,
         ),
       ],
     );
@@ -180,6 +193,12 @@ class _NotificationsTabState extends ConsumerState<NotificationsTab> {
         },
         'digestFrequency': _digestFrequency,
       });
+      // Update saved snapshot so Cancel won't revert after successful save
+      _originalPrefs = {
+        for (final e in _notificationPrefs.entries)
+          e.key: Map<String, bool>.from(e.value),
+      };
+      _originalFrequency = _digestFrequency;
       _showSnackBar('Notification settings saved');
     } catch (e) {
       _showSnackBar('Failed to save: $e', isError: true);