feat(flutter/player): mini PlayerBar in shell + tap-to-play wiring

PlayerBar reads playbackState + mediaItem streams; hidden when no
queue. Home track-row tap, album play button, album track tap, artist
play button (shuffle) all route to playerActions.playTracks. Token +
baseUrl forwarded to the audio handler before each new queue.

flutter_client/lib/library/album_detail_screen.dart

@@ -3,6 +3,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 
 import '../api/endpoints/likes.dart';
 import '../likes/like_button.dart';
+import '../player/player_provider.dart';
 import '../theme/theme_extension.dart';
 import 'library_providers.dart';
 import 'widgets/track_row.dart';
@@ -42,7 +43,7 @@ class AlbumDetailScreen extends ConsumerWidget {
                     decoration: BoxDecoration(color: fs.accent, shape: BoxShape.circle),
                     child: IconButton(
                       icon: Icon(Icons.play_arrow, color: fs.parchment),
-                      onPressed: () { /* play wired in Task 18 */ },
+                      onPressed: () => ref.read(playerActionsProvider).playTracks(r.tracks),
                     ),
                   ),
                   LikeButton(kind: LikeKind.album, id: r.album.id, size: 28),
@@ -51,7 +52,10 @@ class AlbumDetailScreen extends ConsumerWidget {
               for (final t in r.tracks)
                 TrackRow(
                   track: t,
-                  onTap: () { /* play wired in Task 18 */ },
+                  onTap: () {
+                    final start = r.tracks.indexOf(t);
+                    ref.read(playerActionsProvider).playTracks(r.tracks, initialIndex: start);
+                  },
                   trailing: LikeButton(kind: LikeKind.track, id: t.id),
                 ),
             ]),

flutter_client/lib/library/artist_detail_screen.dart

@@ -5,6 +5,7 @@ import 'package:go_router/go_router.dart';
 import '../api/endpoints/likes.dart';
 import '../likes/like_button.dart';
 import '../models/album.dart';
+import '../player/player_provider.dart';
 import '../theme/theme_extension.dart';
 import 'library_providers.dart';
 import 'widgets/album_card.dart';
@@ -49,7 +50,12 @@ class ArtistDetailScreen extends ConsumerWidget {
                 decoration: BoxDecoration(color: fs.accent, shape: BoxShape.circle),
                 child: IconButton(
                   icon: Icon(Icons.play_arrow, color: fs.parchment),
-                  onPressed: () { /* play wired in Task 18 */ },
+                  onPressed: () async {
+                    final tracks = await ref.read(artistTracksProvider(id).future);
+                    if (tracks.isEmpty) return;
+                    final shuffled = [...tracks]..shuffle();
+                    ref.read(playerActionsProvider).playTracks(shuffled);
+                  },
                 ),
               ),
               LikeButton(kind: LikeKind.artist, id: a.id, size: 28),

flutter_client/lib/library/home_screen.dart

@@ -5,6 +5,7 @@ import 'package:go_router/go_router.dart';
 import '../models/album.dart';
 import '../models/artist.dart';
 import '../models/track.dart';
+import '../player/player_provider.dart';
 import '../theme/theme_extension.dart';
 import 'library_providers.dart';
 import 'widgets/album_card.dart';
@@ -66,7 +67,10 @@ class HomeScreen extends ConsumerWidget {
           for (final t in tracks)
             SizedBox(
               width: 280,
-              child: TrackRow(track: t, onTap: () { /* play wired in Task 18 */ }),
+              child: TrackRow(
+                track: t,
+                onTap: () => ref.read(playerActionsProvider).playTracks([t]),
+              ),
             ),
         ],
       );