Auto dark/bright follows the sun at the tablet's own location

Without a light sensor an app may read (the Redmi Pad SE has none), auto is dark while
the sun is more than 4° below the horizon (lib/theme/sun.dart), at Android's coarse
location, polled and kept across restarts. The tablet's own, not the Orin's GNSS: the
tablet has its own GNSS and cellular. Android's dark theme is the last fallback.

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

lib/main.dart

@@ -1,16 +1,18 @@
 // Yukart display: the tablet app. Starts the link to the Orin and hands the screen to
 // the shell (lib/shell.dart). Code layout: lib/README.md.
 
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 
 import 'link/boundary.dart';
 import 'link/net.dart';
-import 'link/reading.dart';
 import 'pages/link_test.dart';
 import 'shell.dart';
 import 'shell_scope.dart';
 import 'theme/light.dart';
 import 'theme/palette.dart';
+import 'theme/sun.dart';
 
 /// Override for development, e.g. `--dart-define=YUKART_GW=ws://halogen.local:7700/`.
 const defaultUrl = String.fromEnvironment(
@@ -25,14 +27,15 @@ Future<void> main() async {
   final usb = UsbLink();
   await usb.bindFor(Uri.parse(defaultUrl));
   final boundary = Boundary(defaultUrl)..start();
-  // The sun, for auto dark/bright: the car's position while GNSS has one.
-  boundary.addListener(() {
-    final lat = Reading.of(boundary, 'gnss_lat');
-    final lon = Reading.of(boundary, 'gnss_lon');
-    if (!lat.dim && !lon.dim && lat.number != null && lon.number != null) {
-      themes.setPosition(lat.number!, lon.number!);
-    }
-  });
+  // The sun, for auto dark/bright: the tablet's own location, every minute until there
+  // is one (the first ask brings up the permission), then every ten.
+  Future<void> locate() async {
+    final p = await androidLocation();
+    if (p != null) themes.setPosition(p.$1, p.$2);
+    Timer(Duration(minutes: p == null ? 1 : 10), locate);
+  }
+
+  locate();
   final linkTest = LinkTest(usb);
   // Development hook: `am start ... --es linktest [dl:|bi:]<label>[@<host>]` runs the test
   // (`dl:` the download series, `bi:` burst latency against idle gaps), on the gateway's host unless one is given.