♿ Make theme switcher easier to use

lib/providers/theme_switcher.dart

@@ -0,0 +1,30 @@
+import 'package:flutter/material.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+import 'package:solian/theme.dart';
+
+class ThemeSwitcher extends ChangeNotifier {
+  ThemeData lightThemeData;
+  ThemeData darkThemeData;
+
+  ThemeSwitcher({
+    required this.lightThemeData,
+    required this.darkThemeData,
+  });
+
+  Future<void> restoreTheme() async {
+    final prefs = await SharedPreferences.getInstance();
+    if (prefs.containsKey('global_theme_color')) {
+      final value = prefs.getInt('global_theme_color')!;
+      final color = Color(value);
+      lightThemeData = SolianTheme.build(Brightness.light, seedColor: color);
+      darkThemeData = SolianTheme.build(Brightness.dark, seedColor: color);
+      notifyListeners();
+    }
+  }
+
+  void setTheme(ThemeData light, dark) {
+    lightThemeData = light;
+    darkThemeData = dark;
+    notifyListeners();
+  }
+}