style: make theme switching inactive and enable light theme by default

Workaround for #144

lib/src/model/app_settings.dart

@@ -4,10 +4,10 @@ import 'package:flutter/material.dart';
 import 'package:quickgui/src/supported_locales.dart';
 
 class AppSettings extends ChangeNotifier {
-  ThemeMode? _themeMode;
+  ThemeMode _themeMode = ThemeMode.light;
   String? _activeLocale;
 
-  ThemeMode get themeMode => _themeMode ?? ThemeMode.system;
+  ThemeMode get themeMode => _themeMode;
 
   String get activeLocale => _activeLocale ?? Platform.localeName;
 
@@ -38,8 +38,7 @@ class AppSettings extends ChangeNotifier {
   }
 
   set useDarkModeSilently(bool useDarkMode) {
-    //_themeMode = useDarkMode ? ThemeMode.dark : ThemeMode.light;
+    _themeMode = useDarkMode ? ThemeMode.dark : ThemeMode.light;
-    _themeMode = ThemeMode.light;
   }
 
   set useDarkMode(bool useDarkMode) {

lib/src/widgets/left_menu.dart

@@ -48,18 +48,27 @@ class _LeftMenuState extends State<LeftMenu> with PreferencesMixin {
                 title: Text("Quickgui $_version",
                     style: Theme.of(context).textTheme.titleLarge),
               ),
-              /*
               const Divider(),
               Padding(
                 padding: const EdgeInsets.symmetric(horizontal: 16),
                 child: Row(
                   children: [
-                    Text(context.t('Use dark mode')),
+                    Text(context.t('Use dark mode'),
+                      style: TextStyle(
+                        color: Colors.grey[300],
+                      ),
+                    ),
                     Expanded(
                       child: Container(),
                     ),
                     Switch(
                       value: Theme.of(context).colorScheme.brightness == Brightness.dark,
+                      onChanged: null,
+                      activeColor: Colors.grey[300],
+                      activeTrackColor: Colors.grey[300],
+                      inactiveThumbColor: Colors.grey[300],
+                      inactiveTrackColor: Colors.grey[300],
+                      /*
                       onChanged: (value) {
                         appSettings.useDarkMode = value;
                         savePreference(prefThemeMode, value);
@@ -68,11 +77,11 @@ class _LeftMenuState extends State<LeftMenu> with PreferencesMixin {
                       activeTrackColor: Colors.black26,
                       inactiveThumbColor: Theme.of(context).colorScheme.onPrimary,
                       inactiveTrackColor: Theme.of(context).colorScheme.primary,
+                      */
                     ),
                   ],
                 ),
               ),
-              */
               const Divider(),
               Padding(
                 padding: const EdgeInsets.symmetric(horizontal: 16),