feat: implement library view with Authors, Genres, and Series browsing

This commit implements a comprehensive library browsing feature:

- Add LibraryBrowserProvider with providers for authors, genres, and series data
- Create LibraryAuthorsPage with grid view of authors including images and book counts
- Create LibraryGenresPage with list view of all genres
- Create LibrarySeriesPage with list view of series and book counts
- Update LibraryBrowserPage navigation to route to the new views
- Add routes for /browser/authors, /browser/genres, and /browser/series
- Replace "Not Implemented" toasts with functional navigation

The implementation uses the Audiobookshelf API via shelfsdk to fetch:
- Authors list with metadata (getAuthors)
- Genres from library filter data (getFilterData)
- Series with pagination support (getSeries)

All views follow Material Design 3 patterns and include proper loading/error states.

lib/router/constants.dart

@@ -82,6 +82,25 @@ class Routes {
     // parentRoute: library,
   );
 
+  // library browser sub-routes
+  static const libraryAuthors = _SimpleRoute(
+    pathName: 'authors',
+    name: 'libraryAuthors',
+    parentRoute: libraryBrowser,
+  );
+
+  static const libraryGenres = _SimpleRoute(
+    pathName: 'genres',
+    name: 'libraryGenres',
+    parentRoute: libraryBrowser,
+  );
+
+  static const librarySeries = _SimpleRoute(
+    pathName: 'series',
+    name: 'librarySeries',
+    parentRoute: libraryBrowser,
+  );
+
   // you page for the user
   static const you = _SimpleRoute(
     pathName: 'you',

lib/router/router.dart

@@ -4,7 +4,10 @@ import 'package:vaani/features/downloads/view/downloads_page.dart';
 import 'package:vaani/features/explore/view/explore_page.dart';
 import 'package:vaani/features/explore/view/search_result_page.dart';
 import 'package:vaani/features/item_viewer/view/library_item_page.dart';
+import 'package:vaani/features/library_browser/view/library_authors_page.dart';
 import 'package:vaani/features/library_browser/view/library_browser_page.dart';
+import 'package:vaani/features/library_browser/view/library_genres_page.dart';
+import 'package:vaani/features/library_browser/view/library_series_page.dart';
 import 'package:vaani/features/logging/view/logs_page.dart';
 import 'package:vaani/features/onboarding/view/callback_page.dart';
 import 'package:vaani/features/onboarding/view/onboarding_single_page.dart';
@@ -121,6 +124,23 @@ class MyAppRouter {
                     path: Routes.libraryBrowser.localPath,
                     name: Routes.libraryBrowser.name,
                     pageBuilder: defaultPageBuilder(const LibraryBrowserPage()),
+                    routes: [
+                      GoRoute(
+                        path: Routes.libraryAuthors.pathName,
+                        name: Routes.libraryAuthors.name,
+                        pageBuilder: defaultPageBuilder(const LibraryAuthorsPage()),
+                      ),
+                      GoRoute(
+                        path: Routes.libraryGenres.pathName,
+                        name: Routes.libraryGenres.name,
+                        pageBuilder: defaultPageBuilder(const LibraryGenresPage()),
+                      ),
+                      GoRoute(
+                        path: Routes.librarySeries.pathName,
+                        name: Routes.librarySeries.name,
+                        pageBuilder: defaultPageBuilder(const LibrarySeriesPage()),
+                      ),
+                    ],
                   ),
                 ],
               ),