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/utils/path_match_keys.dart

@@ -22,6 +22,9 @@ const _audioExtensions = <String>[
   '.aac',
 ];
 
+const _maxPathMatchKeyCacheSize = 6000;
+final Map<String, Set<String>> _pathMatchKeyCache = <String, Set<String>>{};
+
 /// Strips a trailing audio extension from [path] if present.
 /// Returns the path without extension, or `null` if no known audio extension
 /// was found.
@@ -41,6 +44,11 @@ Set<String> buildPathMatchKeys(String? filePath) {
 
   final cleaned = raw.startsWith('EXISTS:') ? raw.substring(7).trim() : raw;
   if (cleaned.isEmpty) return const {};
+  final cached = _pathMatchKeyCache.remove(cleaned);
+  if (cached != null) {
+    _pathMatchKeyCache[cleaned] = cached;
+    return cached;
+  }
 
   final keys = <String>{};
   final visited = <String>{};
@@ -118,7 +126,12 @@ Set<String> buildPathMatchKeys(String? filePath) {
   }
   keys.addAll(extensionStrippedKeys);
 
-  return keys;
+  final result = Set<String>.unmodifiable(keys);
+  _pathMatchKeyCache[cleaned] = result;
+  while (_pathMatchKeyCache.length > _maxPathMatchKeyCacheSize) {
+    _pathMatchKeyCache.remove(_pathMatchKeyCache.keys.first);
+  }
+  return result;
 }
 
 Iterable<String> _androidEquivalentPaths(String path) {