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>

test/palette_test.dart

@@ -1,3 +1,6 @@
+import 'dart:async';
+
+import 'package:display/theme/light.dart';
 import 'package:display/theme/palette.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -33,4 +36,38 @@ void main() {
       expect(make().mode, VariantMode.dark); // kept for the next start
     },
   );
+
+  test('the light switch has a gap and a hold', () {
+    final s = LightSwitch();
+    final t0 = DateTime(2026);
+    DateTime at(int sec) => t0.add(Duration(seconds: sec));
+    expect(s.feed(30, at(0)), isNull); // in the gap: no verdict yet
+    expect(s.feed(500, at(1)), isFalse); // the first clear reading decides
+    expect(s.feed(30, at(2)), isFalse); // the gap keeps it
+    expect(s.feed(5, at(3)), isFalse); // dark, but not for long enough
+    expect(s.pending, isTrue);
+    expect(s.feed(200, at(4)), isFalse); // back: the hold restarts
+    expect(s.pending, isFalse);
+    s.feed(5, at(10));
+    expect(s.feed(5, at(14)), isFalse);
+    expect(s.feed(5, at(15)), isTrue);
+  });
+
+  testWidgets('auto takes the light sensor over Android', (tester) async {
+    SharedPreferences.setMockInitialValues({});
+    final prefs = await SharedPreferences.getInstance();
+    tester.platformDispatcher.platformBrightnessTestValue = Brightness.dark;
+    final t = Themes('t', Palette.fallbackDark, Palette.fallbackBright, prefs);
+    final levels = StreamController<double>();
+    t.followLight(levels.stream);
+    expect(t.isDark, isTrue); // no reading yet: Android's
+    levels.add(800);
+    await tester.pump();
+    expect((t.isDark, t.lux.value), (false, 800));
+    levels.add(2);
+    await tester.pump(
+      const Duration(seconds: 6),
+    ); // no new reading: the timer ends the hold
+    expect(t.isDark, isTrue);
+  });
 }