feat(flutter/library): card + row widgets (artist/album/track)

HorizontalScrollRow takes an optional shared ScrollController so
multi-row sections (Most played: 3 rows) couple their scroll like the
web HorizontalScrollRow.svelte. Cards fall back to the synced
album-fallback.svg when coverUrl is empty.

flutter_client/lib/library/widgets/album_card.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_svg/flutter_svg.dart';
+
+import '../../models/album.dart';
+import '../../theme/theme_extension.dart';
+
+class AlbumCard extends StatelessWidget {
+  const AlbumCard({required this.album, required this.onTap, super.key});
+  final AlbumRef album;
+  final VoidCallback onTap;
+
+  @override
+  Widget build(BuildContext context) {
+    final fs = Theme.of(context).extension<FabledSwordTheme>()!;
+    return GestureDetector(
+      onTap: onTap,
+      child: SizedBox(
+        width: 140,
+        child: Padding(
+          padding: const EdgeInsets.symmetric(horizontal: 8),
+          child: Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
+            ClipRRect(
+              borderRadius: BorderRadius.circular(6),
+              child: Container(
+                width: 124,
+                height: 124,
+                color: fs.slate,
+                child: album.coverUrl.isEmpty
+                    ? SvgPicture.asset('assets/svg/album-fallback.svg', fit: BoxFit.cover)
+                    : Image.network(album.coverUrl, fit: BoxFit.cover),
+              ),
+            ),
+            const SizedBox(height: 8),
+            Text(
+              album.title,
+              maxLines: 1,
+              overflow: TextOverflow.ellipsis,
+              style: TextStyle(color: fs.parchment, fontSize: 14),
+            ),
+            Text(
+              album.artistName,
+              maxLines: 1,
+              overflow: TextOverflow.ellipsis,
+              style: TextStyle(color: fs.ash, fontSize: 12),
+            ),
+          ]),
+        ),
+      ),
+    );
+  }
+}

flutter_client/lib/library/widgets/artist_card.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_svg/flutter_svg.dart';
+
+import '../../models/artist.dart';
+import '../../theme/theme_extension.dart';
+
+class ArtistCard extends StatelessWidget {
+  const ArtistCard({required this.artist, required this.onTap, super.key});
+  final ArtistRef artist;
+  final VoidCallback onTap;
+
+  @override
+  Widget build(BuildContext context) {
+    final fs = Theme.of(context).extension<FabledSwordTheme>()!;
+    return GestureDetector(
+      onTap: onTap,
+      child: SizedBox(
+        width: 140,
+        child: Padding(
+          padding: const EdgeInsets.symmetric(horizontal: 8),
+          child: Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
+            ClipOval(
+              child: Container(
+                width: 124,
+                height: 124,
+                color: fs.slate,
+                child: artist.coverUrl.isEmpty
+                    ? SvgPicture.asset('assets/svg/album-fallback.svg', fit: BoxFit.cover)
+                    : Image.network(artist.coverUrl, fit: BoxFit.cover),
+              ),
+            ),
+            const SizedBox(height: 8),
+            Text(
+              artist.name,
+              maxLines: 1,
+              overflow: TextOverflow.ellipsis,
+              style: TextStyle(color: fs.parchment, fontSize: 14),
+            ),
+          ]),
+        ),
+      ),
+    );
+  }
+}

flutter_client/lib/library/widgets/horizontal_scroll_row.dart

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+import 'package:flutter/material.dart';
+
+import '../../theme/theme_extension.dart';
+
+/// Mirrors the web HorizontalScrollRow: a labeled section that scrolls
+/// horizontally. Multi-row sections share one [controller] so they
+/// scroll together.
+class HorizontalScrollRow extends StatelessWidget {
+  const HorizontalScrollRow({
+    required this.title,
+    required this.children,
+    this.height = 200,
+    this.controller,
+    super.key,
+  });
+
+  final String title;
+  final List<Widget> children;
+  final double height;
+  final ScrollController? controller;
+
+  @override
+  Widget build(BuildContext context) {
+    final fs = Theme.of(context).extension<FabledSwordTheme>()!;
+    return Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
+      Padding(
+        padding: const EdgeInsets.fromLTRB(16, 8, 16, 8),
+        child: Text(
+          title,
+          style: TextStyle(
+            fontFamily: fs.display.fontFamily,
+            fontSize: 18,
+            color: fs.parchment,
+          ),
+        ),
+      ),
+      SizedBox(
+        height: height,
+        child: ListView(
+          controller: controller,
+          scrollDirection: Axis.horizontal,
+          padding: const EdgeInsets.symmetric(horizontal: 16),
+          children: children,
+        ),
+      ),
+    ]);
+  }
+}

flutter_client/lib/library/widgets/track_row.dart

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+import 'package:flutter/material.dart';
+
+import '../../models/track.dart';
+import '../../theme/theme_extension.dart';
+
+class TrackRow extends StatelessWidget {
+  const TrackRow({
+    required this.track,
+    required this.onTap,
+    this.trailing,
+    super.key,
+  });
+  final TrackRef track;
+  final VoidCallback onTap;
+  final Widget? trailing;
+
+  @override
+  Widget build(BuildContext context) {
+    final fs = Theme.of(context).extension<FabledSwordTheme>()!;
+    final mins = (track.durationSec ~/ 60).toString().padLeft(2, '0');
+    final secs = (track.durationSec % 60).toString().padLeft(2, '0');
+    return InkWell(
+      onTap: onTap,
+      child: Padding(
+        padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 10),
+        child: Row(children: [
+          if (track.trackNumber != null)
+            SizedBox(
+              width: 28,
+              child: Text(
+                track.trackNumber.toString(),
+                style: TextStyle(color: fs.ash, fontSize: 13),
+              ),
+            ),
+          Expanded(
+            child: Column(crossAxisAlignment: CrossAxisAlignment.start, children: [
+              Text(
+                track.title,
+                maxLines: 1,
+                overflow: TextOverflow.ellipsis,
+                style: TextStyle(color: fs.parchment, fontSize: 14),
+              ),
+              Text(
+                track.artistName,
+                maxLines: 1,
+                overflow: TextOverflow.ellipsis,
+                style: TextStyle(color: fs.ash, fontSize: 12),
+              ),
+            ]),
+          ),
+          Text('$mins:$secs', style: TextStyle(color: fs.ash, fontSize: 12)),
+          if (trailing != null)
+            Padding(
+              padding: const EdgeInsets.only(left: 8),
+              child: trailing!,
+            ),
+        ]),
+      ),
+    );
+  }
+}

flutter_client/test/library/widgets_smoke_test.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:minstrel/library/widgets/album_card.dart';
+import 'package:minstrel/library/widgets/track_row.dart';
+import 'package:minstrel/models/album.dart';
+import 'package:minstrel/models/track.dart';
+import 'package:minstrel/theme/theme_data.dart';
+
+void main() {
+  testWidgets('AlbumCard renders title and artist', (tester) async {
+    await tester.pumpWidget(MaterialApp(
+      theme: buildThemeData(),
+      home: Scaffold(
+        body: AlbumCard(
+          album: const AlbumRef(
+            id: 'a',
+            title: 'Geogaddi',
+            artistId: 'x',
+            artistName: 'Boards of Canada',
+          ),
+          onTap: () {},
+        ),
+      ),
+    ));
+    expect(find.text('Geogaddi'), findsOneWidget);
+    expect(find.text('Boards of Canada'), findsOneWidget);
+  });
+
+  testWidgets('TrackRow shows mm:ss duration', (tester) async {
+    await tester.pumpWidget(MaterialApp(
+      theme: buildThemeData(),
+      home: Scaffold(
+        body: TrackRow(
+          track: const TrackRef(
+            id: 't',
+            title: 'Roygbiv',
+            albumId: 'a',
+            artistId: 'x',
+            durationSec: 137,
+            trackNumber: 4,
+          ),
+          onTap: () {},
+        ),
+      ),
+    ));
+    expect(find.text('02:17'), findsOneWidget);
+  });
+}