fix(ios): scan app documents without the Files folder picker

lib/widgets/ios_library_folder_sheet.dart

@@ -0,0 +1,52 @@
+import 'package:flutter/material.dart';
+import 'package:path_provider/path_provider.dart';
+import 'package:spotiflac_android/l10n/l10n.dart';
+import 'package:spotiflac_android/services/platform_bridge.dart';
+import 'package:spotiflac_android/widgets/app_bottom_sheet.dart';
+
+enum _LibraryFolderLocation { documents, files }
+
+/// App-owned music does not need a grant from the system Files picker.
+Future<IosPickedDirectory?> showIosLibraryFolderSheet(
+  BuildContext context,
+) async {
+  final location = await showAppModalBottomSheet<_LibraryFolderLocation>(
+    context: context,
+    useRootNavigator: true,
+    builder: (context) => AppBottomSheet(
+      title: context.l10n.libraryAddFolder,
+      child: SingleChildScrollView(
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            AppSheetOption(
+              leading: const Icon(Icons.folder_special_outlined),
+              title: Text(context.l10n.setupAppDocumentsFolder),
+              subtitle: Text(context.l10n.setupAppDocumentsFolderSubtitle),
+              onTap: () =>
+                  Navigator.pop(context, _LibraryFolderLocation.documents),
+            ),
+            AppSheetOption(
+              leading: const Icon(Icons.folder_open_outlined),
+              title: Text(context.l10n.setupChooseFromFiles),
+              subtitle: Text(context.l10n.setupChooseFromFilesSubtitle),
+              onTap: () => Navigator.pop(context, _LibraryFolderLocation.files),
+            ),
+            const SizedBox(height: 8),
+          ],
+        ),
+      ),
+    ),
+  );
+  if (location == null || !context.mounted) return null;
+  if (location == _LibraryFolderLocation.files) {
+    // Keep the native picker and its bookmark for folders outside our sandbox.
+    return PlatformBridge.pickIosDirectory();
+  }
+
+  // Scan Documents recursively, including the SpotiFLAC subfolder created by
+  // setup and music the user copied into the app through Files. No bookmark is
+  // needed: app-owned paths can be rebased when iOS relocates the container.
+  final documents = await getApplicationDocumentsDirectory();
+  return IosPickedDirectory(path: documents.path, bookmark: '');
+}