fix(ci): golangci-lint v2 schema + Flutter 3.44 ListTile strictness

Two fixes for CI bounces caused by the new ci-go:1.26 / ci-flutter:3.44
toolchain images surfacing stricter checks than the previous runners.

1. .golangci.yml: migrate to v2 schema
   - Add `version: "2"` (now required).
   - `linters.disable-all: true` → `linters.default: none`.
   - Move `gofmt` + `goimports` out of `linters` into the new
     top-level `formatters:` block (v2 separates linters and
     formatters).
   - Nest `linters-settings:` under `linters.settings:`.
   - Drop the v1-only `issues.exclude-use-default: false`
     (v2 default exclusion behavior is what we want).

2. Flutter 3.44 made ListTile-inside-ColoredBox a hard assertion
   (was a warning before). Both bottom sheets in track_actions/
   set Container.color on the outer surface, which inserts a
   ColoredBox above their ListTiles. Wrap each ListTile in
   `Material(type: MaterialType.transparency)` so it has an ink
   target beneath the outer color paint without changing the
   visual surface:
   - track_actions_sheet.dart `_MenuItem.build`
   - add_to_playlist_sheet.dart inner ListTile

5 failing widget tests should pass with this change. Local task #70.

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

flutter_client/lib/shared/widgets/track_actions/add_to_playlist_sheet.dart

@@ -69,18 +69,24 @@ class AddToPlaylistSheet extends ConsumerWidget {
                     itemCount: owned.length,
                     itemBuilder: (_, i) {
                       final p = owned[i];
-                      return ListTile(
-                        key: Key('add_to_playlist_${p.id}'),
-                        leading: Icon(LucideIcons.list_music, color: fs.parchment),
-                        title: Text(
-                          p.name,
-                          style: TextStyle(color: fs.parchment),
+                      // Material(transparency) gives ListTile an ink target
+                      // beneath the outer Container's color paint — required
+                      // by the Flutter 3.44 ListTile/ColoredBox assertion.
+                      return Material(
+                        type: MaterialType.transparency,
+                        child: ListTile(
+                          key: Key('add_to_playlist_${p.id}'),
+                          leading: Icon(LucideIcons.list_music, color: fs.parchment),
+                          title: Text(
+                            p.name,
+                            style: TextStyle(color: fs.parchment),
+                          ),
+                          subtitle: Text(
+                            '${p.trackCount} ${p.trackCount == 1 ? "track" : "tracks"}',
+                            style: TextStyle(color: fs.ash, fontSize: 12),
+                          ),
+                          onTap: () => Navigator.pop(context, p.id),
                         ),
-                        subtitle: Text(
-                          '${p.trackCount} ${p.trackCount == 1 ? "track" : "tracks"}',
-                          style: TextStyle(color: fs.ash, fontSize: 12),
-                        ),
-                        onTap: () => Navigator.pop(context, p.id),
                       );
                     },
                   );

flutter_client/lib/shared/widgets/track_actions/track_actions_sheet.dart

@@ -236,10 +236,17 @@ class _MenuItem extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final fs = Theme.of(context).extension<FabledSwordTheme>()!;
-    return ListTile(
-      leading: Icon(icon, color: fs.parchment),
-      title: Text(label, style: TextStyle(color: fs.parchment)),
-      onTap: onTap,
+    // Transparency-typed Material sits between the outer Container's color
+    // paint and the ListTile so ListTile can paint its own ink splashes.
+    // Flutter 3.44 promoted the "ListTile inside ColoredBox without Material"
+    // warning to a hard assertion.
+    return Material(
+      type: MaterialType.transparency,
+      child: ListTile(
+        leading: Icon(icon, color: fs.parchment),
+        title: Text(label, style: TextStyle(color: fs.parchment)),
+        onTap: onTap,
+      ),
     );
   }
 }