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/settings/settings_screen.dart

@@ -1,5 +1,6 @@
 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:go_router/go_router.dart';
 
@@ -37,7 +38,7 @@ class SettingsScreen extends ConsumerWidget {
         backgroundColor: fs.obsidian,
         elevation: 0,
         leading: IconButton(
-          icon: Icon(Icons.arrow_back, color: fs.parchment),
+          icon: Icon(LucideIcons.arrow_left, color: fs.parchment),
           onPressed: () => context.pop(),
         ),
         title: Text('Settings', style: TextStyle(color: fs.parchment)),
@@ -107,7 +108,7 @@ class _RequestsSection extends StatelessWidget {
     final fs = Theme.of(context).extension<FabledSwordTheme>()!;
     return ListTile(
       key: const Key('settings_requests_card'),
-      leading: Icon(Icons.queue_music, color: fs.parchment),
+      leading: Icon(LucideIcons.list_music, color: fs.parchment),
       title: Text(
         'My requests',
         style: TextStyle(
@@ -120,7 +121,7 @@ class _RequestsSection extends StatelessWidget {
         "Track what you've asked Minstrel to add",
         style: TextStyle(color: fs.ash),
       ),
-      trailing: Icon(Icons.chevron_right, color: fs.ash),
+      trailing: Icon(LucideIcons.chevron_right, color: fs.ash),
       onTap: () => context.push('/requests'),
     );
   }
@@ -143,7 +144,7 @@ class _AdminSection extends ConsumerWidget {
         const _Divider(),
         ListTile(
           key: const Key('settings_admin_card'),
-          leading: Icon(Icons.shield, color: fs.parchment),
+          leading: Icon(LucideIcons.shield, color: fs.parchment),
           title: Text(
             'Admin',
             style: TextStyle(
@@ -156,7 +157,7 @@ class _AdminSection extends ConsumerWidget {
             'Manage requests, quarantine, and users',
             style: TextStyle(color: fs.ash),
           ),
-          trailing: Icon(Icons.chevron_right, color: fs.ash),
+          trailing: Icon(LucideIcons.chevron_right, color: fs.ash),
           onTap: () => context.push('/admin'),
         ),
       ],