feat(flutter): bump deps to latest + Search screen slice

Major version bumps (riverpod 2->3, go_router 14->17, just_audio 0.9->0.10,
flutter_secure_storage 9->10, google_fonts 6->8, flutter_lints 4->6).
package_info_plus held at 8.x due to win32 conflict with secure_storage 10.x.

Riverpod 3 breaks: AsyncValue.valueOrNull -> .value, StateProvider replaced
with Notifier subclass. just_audio 0.10: ConcatenatingAudioSource -> setAudioSources.

Search slice:
- models/page.dart (generic Page<T> envelope)
- models/search_response.dart (3-facet wrapper)
- api/endpoints/search.dart
- search/search_provider.dart (debounced 250ms)
- search/search_screen.dart (TextField + 3 horizontal/vertical sections)
- Wired /search route + search button on home AppBar

flutter_client/lib/library/home_screen.dart

@@ -24,6 +24,18 @@ class HomeScreen extends ConsumerWidget {
     final fs = Theme.of(context).extension<FabledSwordTheme>()!;
     return Scaffold(
       backgroundColor: fs.obsidian,
+      appBar: AppBar(
+        backgroundColor: fs.obsidian,
+        elevation: 0,
+        title: Text('Minstrel', style: TextStyle(color: fs.parchment)),
+        actions: [
+          IconButton(
+            icon: Icon(Icons.search, color: fs.parchment),
+            tooltip: 'Search',
+            onPressed: () => context.push('/search'),
+          ),
+        ],
+      ),
       body: SafeArea(
         child: ref.watch(homeProvider).when(
               error: (e, _) {