perf: lazy extension VM init, incremental startup maintenance, and UI optimizations

- Defer extension VM initialization until first use with lockReadyVM() pattern to eliminate TOCTOU races and reduce startup overhead
- Add validateExtensionLoad() to catch JS errors at install time without keeping VM alive
- Teardown VM on extension disable to free resources; re-init lazily on re-enable
- Replace full orphan cleanup with incremental cursor-based pagination across launches
- Batch DB writes (upsertBatch, replaceAll) with transactions for atomicity
- Parse JSON natively on Kotlin side to avoid double-serialization over MethodChannel
- Add identity-based memoization caches for unified items and path match keys in queue tab
- Use ValueListenableBuilder for targeted embedded cover refreshes instead of full setState
- Extract shared widgets (_buildAlbumGridItemCore, _buildFilterButton, _navigateWithUnfocus)
- Use libraryCollectionsProvider selector and MediaQuery.paddingOf for fewer rebuilds
- Simplify supporter chip tiers and localize remaining hardcoded strings

lib/widgets/bottom_sheet_option_tile.dart

@@ -0,0 +1,40 @@
+import 'package:flutter/material.dart';
+
+/// Reusable option tile for bottom sheets.
+/// Used in playlist options, track options, cover options, etc.
+class BottomSheetOptionTile extends StatelessWidget {
+  final IconData icon;
+  final Color? iconColor;
+  final String title;
+  final VoidCallback onTap;
+
+  const BottomSheetOptionTile({
+    super.key,
+    required this.icon,
+    this.iconColor,
+    required this.title,
+    required this.onTap,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final colorScheme = Theme.of(context).colorScheme;
+    return ListTile(
+      contentPadding: const EdgeInsets.symmetric(horizontal: 24, vertical: 4),
+      leading: Container(
+        padding: const EdgeInsets.all(10),
+        decoration: BoxDecoration(
+          color: colorScheme.primaryContainer,
+          borderRadius: BorderRadius.circular(12),
+        ),
+        child: Icon(
+          icon,
+          color: iconColor ?? colorScheme.onPrimaryContainer,
+          size: 20,
+        ),
+      ),
+      title: Text(title, style: const TextStyle(fontWeight: FontWeight.w500)),
+      onTap: onTap,
+    );
+  }
+}

lib/widgets/download_service_picker.dart

@@ -303,7 +303,9 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
                     ),
                   for (final ext in downloadExtensions)
                     _ServiceChip(
-                      label: ext.displayName,
+                      label: widget.recommendedService == ext.id
+                          ? '${ext.displayName} (Recommended)'
+                          : ext.displayName,
                       isSelected: _selectedService == ext.id,
                       onTap: () => setState(() => _selectedService = ext.id),
                       iconPath: ext.iconPath,