fix(config): default API URLs to https schweitz.net domains

Browser clients run on machines other than the host, and the homelab is
retiring direct LAN IP:port access (ports move to loopback behind NPM),
so the 192.168.86.149 defaults would stop working. The public domains
work from anywhere; LAN clients bypass Authentik via source-IP rules.
LAN development can still override via --dart-define.

Portainer (9000) and Netdata (19999) defaults are left unchanged: no
*.schweitz.net proxy hosts exist for those services yet.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/core/config/app_config_test.dart

@@ -0,0 +1,15 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tatlock_ui/core/config/app_config.dart';
+
+void main() {
+  group('AppConfig', () {
+    test('defaults to public schweitz.net API URLs', () {
+      expect(AppConfig.coreApiUrl, 'https://api.schweitz.net');
+      expect(AppConfig.tatlockApiUrl, 'https://tatlock.schweitz.net');
+    });
+
+    test('requiresAuth is true with default schweitz.net URLs', () {
+      expect(AppConfig.requiresAuth, isTrue);
+    });
+  });
+}