feat(flutter/player): NowPlaying full-screen view with scrubber

Reached by tapping the PlayerBar. Reads media + playback streams; seek
dispatches through the audio handler. Swipe-down dismiss is a stand-in
chevron-down AppBar leading icon for v1.

flutter_client/lib/player/now_playing_screen.dart

@@ -0,0 +1,75 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../theme/theme_extension.dart';
+import 'player_provider.dart';
+
+class NowPlayingScreen extends ConsumerWidget {
+  const NowPlayingScreen({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final fs = Theme.of(context).extension<FabledSwordTheme>()!;
+    final media = ref.watch(mediaItemProvider).valueOrNull;
+    final playback = ref.watch(playbackStateProvider).valueOrNull;
+
+    if (media == null) {
+      return const Scaffold(body: Center(child: Text('Nothing playing.')));
+    }
+
+    final pos = playback?.updatePosition ?? Duration.zero;
+    final dur = media.duration ?? Duration.zero;
+
+    return Scaffold(
+      backgroundColor: fs.obsidian,
+      appBar: AppBar(
+        backgroundColor: fs.obsidian,
+        leading: IconButton(
+          icon: Icon(Icons.expand_more, color: fs.parchment),
+          onPressed: () => Navigator.of(context).pop(),
+        ),
+      ),
+      body: SafeArea(
+        child: Padding(
+          padding: const EdgeInsets.all(24),
+          child: Column(children: [
+            const Spacer(),
+            Container(
+              width: 280, height: 280, color: fs.slate,
+            ),
+            const SizedBox(height: 24),
+            Text(media.title, style: TextStyle(color: fs.parchment, fontSize: 22)),
+            Text(media.artist ?? '', style: TextStyle(color: fs.ash, fontSize: 14)),
+            const SizedBox(height: 16),
+            Slider(
+              activeColor: fs.accent,
+              min: 0,
+              max: dur.inMilliseconds.toDouble().clamp(1, double.infinity),
+              value: pos.inMilliseconds.toDouble().clamp(0, dur.inMilliseconds.toDouble()),
+              onChanged: (v) => ref.read(audioHandlerProvider).seek(Duration(milliseconds: v.toInt())),
+            ),
+            Row(mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [
+              IconButton(
+                icon: Icon(Icons.skip_previous, color: fs.parchment, size: 32),
+                onPressed: () => ref.read(audioHandlerProvider).skipToPrevious(),
+              ),
+              IconButton(
+                iconSize: 56,
+                icon: Icon(playback?.playing == true ? Icons.pause_circle_filled : Icons.play_circle_filled, color: fs.accent),
+                onPressed: () {
+                  final h = ref.read(audioHandlerProvider);
+                  if (playback?.playing == true) { h.pause(); } else { h.play(); }
+                },
+              ),
+              IconButton(
+                icon: Icon(Icons.skip_next, color: fs.parchment, size: 32),
+                onPressed: () => ref.read(audioHandlerProvider).skipToNext(),
+              ),
+            ]),
+            const Spacer(),
+          ]),
+        ),
+      ),
+    );
+  }
+}

flutter_client/lib/shared/routing.dart

@@ -8,6 +8,7 @@ import '../auth/server_url_screen.dart';
 import '../library/album_detail_screen.dart';
 import '../library/artist_detail_screen.dart';
 import '../library/home_screen.dart';
+import '../player/now_playing_screen.dart';
 import '../player/player_bar.dart';
 import 'widgets/version_gate.dart';
 
@@ -43,6 +44,7 @@ GoRouter buildRouter(Ref ref) {
             path: '/albums/:id',
             builder: (_, s) => AlbumDetailScreen(id: s.pathParameters['id']!),
           ),
+          GoRoute(path: '/now-playing', builder: (_, __) => const NowPlayingScreen()),
         ],
       ),
     ],