Implement AdminPermissionsScreen, RescanScreen, and TrashScreen (eb)

Add three admin-only screens with routes and navigation tiles:
- AdminPermissionsScreen: permission matrix (users × sets) with optimistic
  grant/revoke checkboxes; admin rows shown as disabled (implicit access).
- AdminRescanScreen: trigger library rescan, poll getScanProgress every 2s
  while running, cancel timer in dispose, show live file/set counters.
- AdminTrashScreen: list soft-deleted media with restore + hard-delete
  (confirmation dialog); optimistic UI with revert-on-error for both actions.
All three use generation counters for stale-async cancellation and guard
async continuations on mounted. Added error mappers and route constants.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/player-android/lib/app_routes.dart b/player-android/lib/app_routes.dart
index 4d31fbd..c07559a 100644
--- a/player-android/lib/app_routes.dart
+++ b/player-android/lib/app_routes.dart
@@ -121,4 +121,20 @@ abstract final class AppRoutes {
   /// Only accessible when the authenticated user has admin privileges.
   /// Shows a list of all registered users and allows creating/deleting accounts.
   static const adminUsers = '/admin/users';
+
+  /// Route for the admin permission matrix screen.
+  ///
+  /// Displays a cross-table of users vs. sets with checkboxes for granting or
+  /// revoking per-user access to each set.  Admin-only.
+  static const adminPermissions = '/admin/permissions';
+
+  /// Route for the admin rescan screen.
+  ///
+  /// Allows an admin to trigger a library rescan and monitor live progress.
+  static const adminRescan = '/admin/rescan';
+
+  /// Route for the admin trash screen.
+  ///
+  /// Lists soft-deleted media items and allows restore or hard-delete.
+  static const adminTrash = '/admin/trash';
 }