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/library/widgets/cached_indicator.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 '../../cache/audio_cache_manager.dart';
@@ -21,7 +22,7 @@ class CachedIndicator extends ConsumerWidget {
         if (snap.data != true) return const SizedBox.shrink();
         return Padding(
           padding: const EdgeInsets.only(left: 4),
-          child: Icon(Icons.download_done, size: 14, color: fs.accent),
+          child: Icon(LucideIcons.circle_check_big, size: 14, color: fs.accent),
         );
       },
     );

flutter_client/lib/library/widgets/play_circle_button.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_lucide/flutter_lucide.dart';
 
 import '../../theme/theme_extension.dart';
 
@@ -85,7 +86,7 @@ class _PlayCircleButtonState extends State<PlayCircleButton> {
                   ),
                 )
               : Icon(
-                  Icons.play_arrow,
+                  LucideIcons.play,
                   color: fs.parchment,
                   size: iconSize,
                 ),