refactor(ui): Lucide migration unit 2 — Icons.* -> LucideIcons.* sweep (#60)

Mechanical sweep across 30 files: every Material Icons.* replaced with
the signed-off Lucide equivalent + a flutter_lucide import per file.
Zero Material Icons.* remain in lib/; no unused imports.

Judgment-call mappings: album->disc_3, library_music->library_big,
playlist_play->list_video, graphic_eq->audio_lines,
system_update->download, restore->archive_restore,
download_done->circle_check_big.

track_actions_sheet like menu row: collapsed `liked ? favorite :
favorite_border` to a single LucideIcons.heart (the row's Like/Unlike
text label conveys state). Icon-only LikeButton + the notification keep
the filled-vs-outline shape per the design decision.

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

flutter_client/lib/playlists/widgets/playlist_card.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_lucide/flutter_lucide.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 
@@ -55,12 +56,12 @@ class PlaylistCard extends ConsumerWidget {
                       // errorBuilder shows the queue_music icon over the
                       // slate background.
                       child: playlist.coverUrl.isEmpty
-                          ? Icon(Icons.queue_music, color: fs.ash, size: 56)
+                          ? Icon(LucideIcons.list_music, color: fs.ash, size: 56)
                           : ServerImage(
                               url: playlist.coverUrl,
                               fit: BoxFit.cover,
                               fallback:
-                                  Icon(Icons.queue_music, color: fs.ash, size: 56),
+                                  Icon(LucideIcons.list_music, color: fs.ash, size: 56),
                             ),
                     ),
                   ),
@@ -80,7 +81,7 @@ class PlaylistCard extends ConsumerWidget {
                       top: 2,
                       right: 2,
                       child: PopupMenuButton<String>(
-                        icon: Icon(Icons.more_vert, color: fs.parchment, size: 18),
+                        icon: Icon(LucideIcons.ellipsis_vertical, color: fs.parchment, size: 18),
                         tooltip: 'Playlist actions',
                         color: fs.iron,
                         onSelected: (_) => _refresh(context, ref),
@@ -88,7 +89,7 @@ class PlaylistCard extends ConsumerWidget {
                           PopupMenuItem<String>(
                             value: 'refresh',
                             child: Row(children: [
-                              Icon(Icons.refresh, color: fs.parchment, size: 18),
+                              Icon(LucideIcons.refresh_cw, color: fs.parchment, size: 18),
                               const SizedBox(width: 8),
                               Text(_refreshLabel,
                                   style: TextStyle(color: fs.parchment)),

flutter_client/lib/playlists/widgets/playlist_placeholder_card.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_lucide/flutter_lucide.dart';
 
 import '../../theme/theme_extension.dart';
 
@@ -65,9 +66,9 @@ class PlaylistPlaceholderCard extends StatelessWidget {
           child: CircularProgressIndicator(strokeWidth: 2, color: fs.accent),
         );
       case 'failed':
-        return Icon(Icons.warning_amber, color: fs.error, size: 32);
+        return Icon(LucideIcons.triangle_alert, color: fs.error, size: 32);
       default:
-        return Icon(Icons.queue_music, color: fs.ash, size: 40);
+        return Icon(LucideIcons.list_music, color: fs.ash, size: 40);
     }
   }