fix；设置和深浅色

lib/theme/theme_controller.dart

@@ -0,0 +1,42 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+import 'package:hooks_riverpod/hooks_riverpod.dart';
+import 'package:shared_preferences/shared_preferences.dart';
+
+const _themeModeKey = 'theme_mode';
+
+final themeModeProvider = StateNotifierProvider<ThemeModeController, ThemeMode>(
+  (ref) => ThemeModeController(),
+);
+
+class ThemeModeController extends StateNotifier<ThemeMode> {
+  ThemeModeController() : super(ThemeMode.system) {
+    unawaited(_loadSavedMode());
+  }
+
+  Future<void> _loadSavedMode() async {
+    final prefs = await SharedPreferences.getInstance();
+    final raw = prefs.getString(_themeModeKey);
+    if (raw == null) return;
+    state = _decode(raw);
+  }
+
+  Future<void> setMode(ThemeMode mode) async {
+    state = mode;
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString(_themeModeKey, _encode(mode));
+  }
+
+  ThemeMode _decode(String raw) => switch (raw) {
+    'light' => ThemeMode.light,
+    'dark' => ThemeMode.dark,
+    _ => ThemeMode.system,
+  };
+
+  String _encode(ThemeMode mode) => switch (mode) {
+    ThemeMode.light => 'light',
+    ThemeMode.dark => 'dark',
+    ThemeMode.system => 'system',
+  };
+}