refactor: codebase review cleanup

lib/mixins/context_menu_tap_mixin.dart

@@ -0,0 +1,26 @@
+import 'package:flutter/material.dart';
+
+import '../widgets/media_context_menu.dart';
+
+/// Tracks tap position and exposes show-context-menu helpers for media cards
+/// that wrap their tappable area in a [MediaContextMenu].
+mixin ContextMenuTapMixin<T extends StatefulWidget> on State<T> {
+  final GlobalKey<MediaContextMenuState> contextMenuKey = GlobalKey<MediaContextMenuState>();
+  Offset? _tapPosition;
+
+  void storeTapPosition(TapDownDetails details) {
+    _tapPosition = details.globalPosition;
+  }
+
+  bool get isContextMenuOpen => contextMenuKey.currentState?.isContextMenuOpen ?? false;
+
+  /// Show at the last tap position (long-press, mouse).
+  void showContextMenuFromTap() {
+    contextMenuKey.currentState?.showContextMenu(context, position: _tapPosition);
+  }
+
+  /// Show without a tap position (keyboard, gamepad).
+  void showContextMenu() {
+    contextMenuKey.currentState?.showContextMenu(context);
+  }
+}

lib/mixins/disposable_change_notifier_mixin.dart

@@ -0,0 +1,22 @@
+import 'package:flutter/foundation.dart';
+
+/// Adds [safeNotifyListeners] which no-ops after [dispose]. Use in providers
+/// that fire from async paths where a late callback could otherwise trip
+/// Flutter's debug-only "used after dispose" assert.
+mixin DisposableChangeNotifierMixin on ChangeNotifier {
+  bool _disposed = false;
+
+  bool get isDisposed => _disposed;
+
+  bool safeNotifyListeners() {
+    if (_disposed) return false;
+    notifyListeners();
+    return true;
+  }
+
+  @override
+  void dispose() {
+    _disposed = true;
+    super.dispose();
+  }
+}

lib/mixins/grid_focus_node_mixin.dart

@@ -19,6 +19,12 @@ mixin GridFocusNodeMixin<T extends StatefulWidget> on State<T> {
     return gridItemFocusNodes.putIfAbsent(index, () => FocusNode(debugLabel: '${prefix}_$index'));
   }
 
+  /// Get the focus node for [index], routing index 0 through [firstNode] when
+  /// the grid pins a dedicated node for the first item (e.g. `firstItemFocusNode`).
+  FocusNode focusNodeForIndex(int index, FocusNode firstNode, {required String prefix}) {
+    return index == 0 ? firstNode : getGridItemFocusNode(index, prefix: prefix);
+  }
+
   /// Record that the item at [index] received focus.
   void trackGridItemFocus(int index, bool hasFocus) {
     if (hasFocus) {