feat: responsive layout tuning, cache management page, and improved recent access UX

- Add responsive scaling across album, artist, playlist, downloaded album, local album, queue, setup, and tutorial screens to prevent overflow on smaller devices
- Add new Storage & Cache management page (Settings > Storage & Cache) with per-category clear and cleanup actions
- Extract normalizedHeaderTopPadding utility for consistent app bar padding
- Improve home search Recent Access behavior: show when focused with empty input, hide stale results during active recent mode
- Add excluded-downloaded-count tracking to local library scan stats
- Add recentEmpty and recentShowAllDownloads l10n keys (EN + ID)
- Add full cache management l10n keys (EN + ID)
- Fix about_page indentation and formatting consistency
- Fix appearance_settings_page formatting
- Fix downloaded_album_screen and local_album_screen formatting and responsive sizing

lib/utils/app_bar_layout.dart

@@ -0,0 +1,17 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/widgets.dart';
+
+const double kNormalizedHeaderTopPadding = 24.0;
+
+double normalizedHeaderTopPadding(
+  BuildContext context, {
+  double max = kNormalizedHeaderTopPadding,
+}) {
+  if (defaultTargetPlatform == TargetPlatform.iOS ||
+      defaultTargetPlatform == TargetPlatform.macOS) {
+    return 0;
+  }
+  final topPadding = MediaQuery.paddingOf(context).top;
+  if (topPadding <= 0) return 0;
+  return topPadding > max ? max : topPadding;
+}