Scalar Presence: brand-panel login (light/dark), Poppins, splash and launcher icons, fixed API base via dart-define, keep-signed-in, Android project

- Login reworked to the Brand panel layout with a dark-theme switch; 'Scalar Presence' two-line wordmark
- Android project now tracked (was gitignored); pins shared_preferences_android 2.4.27 (2.5.0 crashed with a black screen)
- API base URL fixed per build (--dart-define=API_BASE_URL), no in-app server setting

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

lib/main.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'api_service.dart';
 import 'settings.dart';
 import 'theme.dart';
+import 'screens/auth_shell.dart';
 import 'screens/login_screen.dart';
 import 'screens/home_screen.dart';
 
@@ -9,6 +10,7 @@ Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
   final settings = Settings();
   await settings.load();
+  if (settings.isLoggedIn && !await KeepSignedIn.wanted()) await settings.clearSession();
   runApp(ScalarEssApp(settings: settings));
 }
 
@@ -20,7 +22,7 @@ class ScalarEssApp extends StatelessWidget {
   Widget build(BuildContext context) {
     final api = ApiService(settings);
     return MaterialApp(
-      title: 'Scalar360 Attendance',
+      title: 'Scalar Presence',
       debugShowCheckedModeBanner: false,
       theme: buildTheme(),
       home: settings.isLoggedIn