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/shared/widgets/version_gate.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 
 import 'package:dio/dio.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter_lucide/flutter_lucide.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:package_info_plus/package_info_plus.dart';
 import 'package:pub_semver/pub_semver.dart';
@@ -238,7 +239,7 @@ class VersionTooOldBanner extends ConsumerWidget {
         color: fs.error.withValues(alpha: 0.15),
         padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 10),
         child: Row(children: [
-          Icon(Icons.warning_amber_rounded, color: fs.error, size: 18),
+          Icon(LucideIcons.triangle_alert, color: fs.error, size: 18),
           const SizedBox(width: 8),
           Expanded(
             child: Text(