Flutter Android login vault: local DB (id+base64 content), email/Google auth, dashboard search/edit/swipe-delete, dark/system theme, minSdk 29

lib/theme_provider.dart

@@ -0,0 +1,40 @@
+import 'package:flutter/material.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+/// Persists and exposes the app theme mode (system | dark).
+class ThemeProvider extends ChangeNotifier {
+  static const _key = 'theme_mode';
+  ThemeMode _mode = ThemeMode.system;
+
+  ThemeProvider() {
+    _load();
+  }
+
+  ThemeMode get mode => _mode;
+
+  Future<void> _load() async {
+    final prefs = await SharedPreferences.getInstance();
+    final v = prefs.getString(_key);
+    if (v == 'dark') {
+      _mode = ThemeMode.dark;
+    } else if (v == 'light') {
+      _mode = ThemeMode.light;
+    } else {
+      _mode = ThemeMode.system;
+    }
+    notifyListeners();
+  }
+
+  Future<void> setMode(ThemeMode mode) async {
+    _mode = mode;
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString(
+        _key,
+        mode == ThemeMode.dark
+            ? 'dark'
+            : mode == ThemeMode.light
+                ? 'light'
+                : 'system');
+    notifyListeners();
+  }
+}