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/utils/contact_filter_types.dart

@@ -0,0 +1,3 @@
+enum ContactSortOption { lastSeen, recentMessages, name }
+
+enum ContactTypeFilter { all, favorites, users, repeaters, rooms }

lib/utils/contact_search.dart

@@ -1,8 +1,6 @@
 import '../models/contact.dart';
 
-enum ContactSortOption { lastSeen, recentMessages, name }
-
-enum ContactTypeFilter { all, favorites, users, repeaters, rooms }
+export 'contact_filter_types.dart';
 
 bool matchesContactQuery(Contact contact, String query) {
   final normalizedQuery = query.trim().toLowerCase();