Auto dark/bright takes a light sensor where the device allows one

lib/theme/light.dart: dark at 15 lux or less, bright from 60, held 5 s; Settings shows the
reading. The Redmi Pad SE refuses apps its only light sensor (Xiaomi's, from the front
camera), so there Auto keeps following Android's dark theme. DASH-NEXT.md records the
other lux sources.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/main.dart

@@ -8,6 +8,7 @@ import 'link/net.dart';
 import 'pages/link_test.dart';
 import 'shell.dart';
 import 'shell_scope.dart';
+import 'theme/light.dart';
 import 'theme/palette.dart';
 
 /// Override for development, e.g. `--dart-define=YUKART_GW=ws://halogen.local:7700/`.
@@ -18,7 +19,8 @@ const defaultUrl = String.fromEnvironment(
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
-  final themes = await Themes.load();
+  final themes = await Themes.load()
+    ..followLight(lightLevels());
   final usb = UsbLink();
   await usb.bindFor(Uri.parse(defaultUrl));
   final boundary = Boundary(defaultUrl)..start();