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/requests/requests_screen.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';
 
@@ -32,7 +33,7 @@ class RequestsScreen 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('Your requests', style: TextStyle(color: fs.parchment)),
@@ -130,9 +131,9 @@ class _RequestRow extends StatelessWidget {
 
   Widget _kindAvatar(FabledSwordTheme fs) {
     final icon = switch (request.kind) {
-      'artist' => Icons.album,
-      'album' => Icons.library_music,
-      _ => Icons.music_note,
+      'artist' => LucideIcons.disc_3,
+      'album' => LucideIcons.library_big,
+      _ => LucideIcons.music,
     };
     return CircleAvatar(
       backgroundColor: fs.iron,
@@ -164,7 +165,7 @@ class _RequestRow extends StatelessWidget {
           );
           if (ok == true) onCancel();
         },
-        icon: const Icon(Icons.close, size: 16),
+        icon: const Icon(LucideIcons.x, size: 16),
         label: const Text('Cancel'),
         style: TextButton.styleFrom(foregroundColor: fs.ash),
       );
@@ -172,7 +173,7 @@ class _RequestRow extends StatelessWidget {
     if (request.status == 'completed' && href != null) {
       return TextButton.icon(
         onPressed: () => context.push(href),
-        icon: const Icon(Icons.play_arrow, size: 16),
+        icon: const Icon(LucideIcons.play, size: 16),
         label: const Text('Listen'),
         style: TextButton.styleFrom(foregroundColor: fs.accent),
       );