fix: migrate filter menus to type-safe generics and harden popup dismissal

- Move ContactSortOption/ContactTypeFilter enums to dedicated
  contact_filter_types.dart (re-exported from contact_search.dart)
- Migrate ContactsFilterMenu and DiscoveryContactsFilterMenu to use
  sealed class action types with SortFilterMenu<T> generics, replacing
  int action constants and switch statements
- Guard _closeDropdownAndRun with ModalRoute.isCurrent check to prevent
  accidental dismissal of parent routes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/screens/contacts_screen.dart

@@ -454,8 +454,11 @@ class _ContactsScreenState extends State<ContactsScreen>
     }
   }
 
-  void _closeDropdownAndRun(BuildContext context, VoidCallback action) {
-    Navigator.of(context).pop();
+  void _closeDropdownAndRun(BuildContext popupContext, VoidCallback action) {
+    final route = ModalRoute.of(popupContext);
+    if (route != null && route.isCurrent) {
+      Navigator.of(popupContext).pop();
+    }
     WidgetsBinding.instance.addPostFrameCallback((_) {
       if (!mounted) return;
       action();