Add go_router + Riverpod wiring and extract SOLID-clean screen/nav layers (na)

Introduces flutter_riverpod and go_router dependencies. Wires up the app
with a Riverpod-managed GoRouter, auth-guarded redirect logic, and a shared
navigator key used by DioClient for 401 → /login redirects.

SOLID fixes applied:
- navigatorKey extracted to navigation_key.dart (DIP: breaks cross-layer
  import from router.dart into api_client_provider.dart)
- AppRoutes extracted to app_routes.dart (SRP + avoids circular import
  when screen files reference route constants)
- LoginScreen, HomeScreen, MediaDetailScreen, ShareScreen each moved to
  their own file under lib/screens/ (SRP: router.dart is routing-only)
- router.dart re-exports AppRoutes for backward-compatible callers

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

1 files changed, 17 insertions, 40 deletions

diff --git a/player-android/lib/main.dart b/player-android/lib/main.dart
index eed6e99..156b8f8 100644
--- a/player-android/lib/main.dart
+++ b/player-android/lib/main.dart
@@ -1,50 +1,27 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
 
-void main() => runApp(const PlayerAndroidApp());
+import 'router.dart';
 
-class PlayerAndroidApp extends StatelessWidget {
-  const PlayerAndroidApp({super.key});
-
-  @override
-  Widget build(BuildContext context) {
-    return MaterialApp(
-      title: 'Player',
-      initialRoute: '/',
-      routes: {
-        '/': (context) => const HomeScreen(),
-        '/now-playing': (context) => const NowPlayingScreen(),
-      },
-    );
-  }
-}
+/// Entry point — wraps the whole widget tree in a [ProviderScope] so every
+/// widget and provider has access to the Riverpod container.
+void main() => runApp(const ProviderScope(child: PlayerAndroidApp()));
 
-// HomeScreen shows the media library. Placeholder until the library API is wired.
-class HomeScreen extends StatelessWidget {
-  const HomeScreen({super.key});
+/// Root application widget.
+///
+/// Uses [ConsumerWidget] to read [routerProvider] from Riverpod so that the
+/// same [GoRouter] instance (and its navigator key) is reused across rebuilds.
+/// [MaterialApp.router] delegates all navigation decisions to go_router.
+class PlayerAndroidApp extends ConsumerWidget {
+  const PlayerAndroidApp({super.key});
 
   @override
-  Widget build(BuildContext context) {
-    return Scaffold(
-      appBar: AppBar(title: const Text('Library')),
-      body: Center(
-        child: ElevatedButton(
-          onPressed: () => Navigator.pushNamed(context, '/now-playing'),
-          child: const Text('Now Playing'),
-        ),
-      ),
-    );
-  }
-}
+  Widget build(BuildContext context, WidgetRef ref) {
+    final router = ref.watch(routerProvider);
 
-// NowPlayingScreen shows the active media item. Placeholder until playback is wired.
-class NowPlayingScreen extends StatelessWidget {
-  const NowPlayingScreen({super.key});
-
-  @override
-  Widget build(BuildContext context) {
-    return Scaffold(
-      appBar: AppBar(title: const Text('Now Playing')),
-      body: const Center(child: Text('No media selected')),
+    return MaterialApp.router(
+      title: 'Player',
+      routerConfig: router,
     );
   }
 }