feat(player): swipe track headers and remove individual queue entries

lib/widgets/player_queue_dismissible.dart

@@ -0,0 +1,41 @@
+import 'package:flutter/material.dart';
+
+/// Removing a row affects the queue only, never the song on disk.
+class PlayerQueueDismissible extends StatelessWidget {
+  const PlayerQueueDismissible({
+    super.key,
+    required this.onRemove,
+    required this.child,
+    this.enabled = true,
+  });
+
+  final VoidCallback onRemove;
+  final Widget child;
+  final bool enabled;
+
+  @override
+  Widget build(BuildContext context) => Dismissible(
+    key: const ValueKey('queue-dismiss'),
+    direction: enabled ? DismissDirection.endToStart : DismissDirection.none,
+    // Remove before collapsing so a concurrently playing row is never left
+    // dismissed in the tree. The service resolves the entry by identity.
+    confirmDismiss: (_) async {
+      onRemove();
+      return false;
+    },
+    background: Container(
+      alignment: AlignmentDirectional.centerEnd,
+      padding: const EdgeInsets.symmetric(horizontal: 20),
+      decoration: BoxDecoration(
+        color: Theme.of(context).colorScheme.error,
+        borderRadius: BorderRadius.circular(12),
+      ),
+      child: Icon(
+        Icons.delete_outline,
+        color: Theme.of(context).colorScheme.onError,
+        semanticLabel: MaterialLocalizations.of(context).deleteButtonTooltip,
+      ),
+    ),
+    child: child,
+  );
+}