Rebrand CommGate to gsmnode and adopt new design system

Rename the whole project from CommGate to gsmnode and re-skin every
surface onto the new signal-green + ink design system (Space Grotesk /
IBM Plex Sans / JetBrains Mono, flat surfaces, two-arrow routing mark,
lowercase gsm+node wordmark).

- Web App + API panel: rewrite token layer, gn-* utilities, data-gsm-theme,
  new logo/favicon assets; both builds verified.
- Phone App (Flutter): green theme, new mark/wordmark widgets, adaptive
  launcher icons; rename Android applicationId/package to app.gsmnode.phone;
  bump AGP to 8.6.0 and google_fonts to 8.1.0; debug APK build verified.
- API Server (Go): panel routes, User-Agent, health service id, branding.
- Home Assistant Plugin: rename integration domain sms_gateway to gsmnode
  (folder, DOMAIN, services, entity ids, classes); py_compile verified.
- Update all READMEs; add .gitignore (excludes Design/, build artifacts).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Phone App/lib/main.dart

@@ -0,0 +1,42 @@
+import 'package:flutter/material.dart';
+
+import 'config.dart';
+import 'services/api_client.dart';
+import 'services/gateway_service.dart';
+import 'services/sms_service.dart';
+import 'services/storage.dart';
+import 'screens/login_screen.dart';
+import 'screens/home_screen.dart';
+import 'theme.dart';
+
+late Storage storage;
+late ApiClient apiClient;
+late GatewayService gateway;
+
+Future<void> main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+
+  storage = await Storage.create();
+  storage.apiBase ??= AppConfig.defaultApiBase;
+
+  apiClient = ApiClient(storage);
+  gateway = GatewayService(apiClient, SmsService());
+
+  runApp(const GsmNodeApp());
+}
+
+class GsmNodeApp extends StatelessWidget {
+  const GsmNodeApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'gsmnode',
+      debugShowCheckedModeBanner: false,
+      theme: gsmnodeLightTheme(),
+      darkTheme: gsmnodeDarkTheme(),
+      themeMode: ThemeMode.system,
+      home: storage.isRegistered ? const HomeScreen() : const LoginScreen(),
+    );
+  }
+}