perf: optimize providers, caching, and reduce rebuilds

- Cache SharedPreferences.getInstance() in providers (settings, theme, recent_access)
- Pre-compute download counts in queue provider to avoid repeated filtering
- Add identical() caching for RecentAccessView in HomeTab
- Use selective watching for exploreProvider (sections, greeting, isLoading only)
- Move isYTMusicQuickPicks computation to ExploreSection.fromJson()
- Hoist static RegExp patterns to avoid repeated compilation
- Use batch operations for iOS path migration in history_database
- Replace containsKey+lookup with single lookup in palette_service
- Pre-compute lowercase strings outside filter loops in logger
- Fix _isLoaded race condition in DownloadHistoryNotifier

lib/services/csv_import_service.dart

@@ -6,6 +6,7 @@ import 'package:spotiflac_android/utils/logger.dart';
 
 class CsvImportService {
   static final _log = AppLogger('CsvImportService');
+  static final RegExp _lineSplitPattern = RegExp(r'\r\n|\r|\n');
 
   static Future<List<Track>> pickAndParseCsv({
     void Function(int current, int total)? onProgress,
@@ -123,7 +124,7 @@ class CsvImportService {
 
   static List<Track> _parseCsv(String content) {
     final List<Track> tracks = [];
-    final lines = content.split(RegExp(r'\r\n|\r|\n'));
+    final lines = content.split(_lineSplitPattern);
     if (lines.isEmpty) return tracks;
 
     int startIdx = 0;

lib/services/history_database.dart

@@ -7,6 +7,7 @@ import 'package:shared_preferences/shared_preferences.dart';
 import 'package:spotiflac_android/utils/logger.dart';
 
 final _log = AppLogger('HistoryDatabase');
+final Future<SharedPreferences> _prefs = SharedPreferences.getInstance();
 
 /// Cached current iOS container path for path normalization
 String? _currentContainerPath;
@@ -135,7 +136,7 @@ class HistoryDatabase {
     await _initContainerPath();
     if (_currentContainerPath == null) return false;
     
-    final prefs = await SharedPreferences.getInstance();
+    final prefs = await _prefs;
     final lastContainer = prefs.getString('ios_last_container_path');
     
     // Skip if container hasn't changed
@@ -152,6 +153,7 @@ class HistoryDatabase {
       // Get all items with iOS paths
       final rows = await db.query('history', columns: ['id', 'file_path']);
       int updatedCount = 0;
+      final batch = db.batch();
       
       for (final row in rows) {
         final id = row['id'] as String;
@@ -160,7 +162,7 @@ class HistoryDatabase {
         if (oldPath != null && _iosContainerPattern.hasMatch(oldPath)) {
           final newPath = _normalizeIosPath(oldPath);
           if (newPath != oldPath) {
-            await db.update(
+            batch.update(
               'history',
               {'file_path': newPath},
               where: 'id = ?',
@@ -171,6 +173,10 @@ class HistoryDatabase {
         }
       }
       
+      if (updatedCount > 0) {
+        await batch.commit(noResult: true);
+      }
+      
       // Save current container path
       await prefs.setString('ios_last_container_path', _currentContainerPath!);
       
@@ -185,7 +191,7 @@ class HistoryDatabase {
   /// Migrate data from SharedPreferences to SQLite
   /// Returns true if migration was performed, false if already migrated
   Future<bool> migrateFromSharedPreferences() async {
-    final prefs = await SharedPreferences.getInstance();
+    final prefs = await _prefs;
     final migrationKey = 'history_migrated_to_sqlite';
     
     if (prefs.getBool(migrationKey) == true) {

lib/services/palette_service.dart

@@ -19,8 +19,9 @@ class PaletteService {
       return null;
     }
 
-    if (_colorCache.containsKey(imageUrl)) {
-      return _colorCache[imageUrl];
+    final cached = _colorCache[imageUrl];
+    if (cached != null) {
+      return cached;
     }
 
     try {

lib/services/share_intent_service.dart

@@ -9,6 +9,12 @@ class ShareIntentService {
   factory ShareIntentService() => _instance;
   ShareIntentService._internal();
 
+  static final RegExp _spotifyUriPattern =
+      RegExp(r'spotify:(track|album|playlist|artist):[a-zA-Z0-9]+');
+  static final RegExp _spotifyUrlPattern = RegExp(
+    r'https?://open\.spotify\.com/(track|album|playlist|artist)/[a-zA-Z0-9]+(\?[^\s]*)?',
+  );
+
   final _sharedUrlController = StreamController<String>.broadcast();
   StreamSubscription<List<SharedMediaFile>>? _mediaSubscription;
   bool _initialized = false;
@@ -57,14 +63,12 @@ class ShareIntentService {
   String? _extractSpotifyUrl(String text) {
     if (text.isEmpty) return null;
 
-    final uriMatch = RegExp(r'spotify:(track|album|playlist|artist):[a-zA-Z0-9]+').firstMatch(text);
+    final uriMatch = _spotifyUriPattern.firstMatch(text);
     if (uriMatch != null) {
       return uriMatch.group(0);
     }
 
-    final urlMatch = RegExp(
-      r'https?://open\.spotify\.com/(track|album|playlist|artist)/[a-zA-Z0-9]+(\?[^\s]*)?',
-    ).firstMatch(text);
+    final urlMatch = _spotifyUrlPattern.firstMatch(text);
     if (urlMatch != null) {
       final fullUrl = urlMatch.group(0)!;
       final queryIndex = fullUrl.indexOf('?');