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/update/update_banner.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 '../theme/theme_extension.dart';
@@ -66,7 +67,7 @@ class _UpdateBannerState extends ConsumerState<UpdateBanner> {
           child: Row(
             crossAxisAlignment: CrossAxisAlignment.center,
             children: [
-              Icon(Icons.system_update, color: fs.parchment, size: 16),
+              Icon(LucideIcons.download, color: fs.parchment, size: 16),
               const SizedBox(width: 8),
               Expanded(
                 child: Column(
@@ -132,7 +133,7 @@ class _UpdateBannerState extends ConsumerState<UpdateBanner> {
                   tooltip: 'Dismiss',
                   padding: EdgeInsets.zero,
                   iconSize: 16,
-                  icon: Icon(Icons.close, color: fs.ash),
+                  icon: Icon(LucideIcons.x, color: fs.ash),
                   onPressed: () => _onDismiss(info),
                 ),
               ),