feat(flutter): full parity for player bar — shuffle/repeat/volume + Like + kebab + 3-column layout (#356)

Mirrors web's compact PlayerBar both visually (3-column top + full-
width seek bottom) and functionally — closes parity gaps that had
been hidden because the prior mini-bar surfaced none of these
controls.

### audio_handler.dart

- Override `setShuffleMode` → delegates to just_audio's
  `setShuffleModeEnabled`.
- Override `setRepeatMode` → maps audio_service modes (none/one/all/
  group) to just_audio's LoopMode (off/one/all).
- New `setVolume(double)` + `volumeStream` getter (audio_service's
  PlaybackState doesn't carry volume — surface it separately).
- `_broadcastState` now populates PlaybackState's shuffleMode +
  repeatMode fields, and re-fires on shuffle/repeat/loop stream
  changes so UI subscribers stay in sync.

### player_provider.dart

- New `volumeProvider` (StreamProvider<double>).
- `PlayerActions` gains `toggleShuffle()`, `cycleRepeat()` (none →
  all → one → none), and `setVolume(double)`.

### player_bar.dart

Complete rebuild matching the operator-designed layout:

  ┌──────────┬───────────┬──────────────────┐
  │ art      │ ♥   ⋮     │ 🔀 🔁 ☰           │  ← short row
  │ title    │           │                  │
  │ artist   │ ⏮  ⏯  ⏭   │ volume slider    │  ← play row, full size
  ├──────────┴───────────┴──────────────────┤
  │ 0:42 ━━━━━●━━━━━━━━━━━━━━━━━━━━━ 3:21  │
  └─────────────────────────────────────────┘

- Column 1 (35%): cover + title + artist. Tap → /now-playing.
- Column 2 (intrinsic): like + kebab on top, play controls (40/48/40)
  on bottom.
- Column 3 (30%): shuffle/repeat/queue on top, volume slider on bottom.
- Bottom: full-width seek slider with mm:ss labels.

`TrackActionsButton` reused for the kebab; reconstructs a minimal
TrackRef from MediaItem extras (same pattern NowPlayingScreen
already uses).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

flutter_client/lib/player/player_provider.dart

@@ -30,6 +30,14 @@ final queueProvider = StreamProvider<List<MediaItem>>(
   (ref) => ref.watch(audioHandlerProvider).queue,
 );
 
+/// Player volume in [0.0, 1.0]. Mirrors just_audio's player.volume;
+/// modify via PlayerActions.setVolume(). Surfaced separately from
+/// PlaybackState because audio_service's PlaybackState doesn't carry
+/// volume — it's a player-side concern.
+final volumeProvider = StreamProvider<double>(
+  (ref) => ref.watch(audioHandlerProvider).volumeStream,
+);
+
 class PlayerActions {
   PlayerActions(this._ref);
   final Ref _ref;
@@ -59,6 +67,32 @@ class PlayerActions {
     final h = _ref.read(audioHandlerProvider);
     await h.enqueue(track);
   }
+
+  /// Toggles shuffle on/off. Pre-existing audio_service convention.
+  Future<void> toggleShuffle() async {
+    final h = _ref.read(audioHandlerProvider);
+    final state = await h.playbackState.first;
+    final next = state.shuffleMode == AudioServiceShuffleMode.none
+        ? AudioServiceShuffleMode.all
+        : AudioServiceShuffleMode.none;
+    await h.setShuffleMode(next);
+  }
+
+  /// Cycles repeat mode: none → all → one → none.
+  Future<void> cycleRepeat() async {
+    final h = _ref.read(audioHandlerProvider);
+    final state = await h.playbackState.first;
+    final next = switch (state.repeatMode) {
+      AudioServiceRepeatMode.none => AudioServiceRepeatMode.all,
+      AudioServiceRepeatMode.all => AudioServiceRepeatMode.one,
+      _ => AudioServiceRepeatMode.none,
+    };
+    await h.setRepeatMode(next);
+  }
+
+  Future<void> setVolume(double v) async {
+    await _ref.read(audioHandlerProvider).setVolume(v);
+  }
 }
 
 final playerActionsProvider = Provider<PlayerActions>((ref) => PlayerActions(ref));