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/config.dart

@@ -0,0 +1,15 @@
+/// Compile-time defaults. The API base URL is also user-editable on the login
+/// screen and persisted via [Storage].
+class AppConfig {
+  /// Default API Server base URL. Use the LAN IP of the machine running the
+  /// API Server (not localhost — that points at the phone itself).
+  ///
+  /// 10.0.2.2 is the Android emulator's alias for the host machine.
+  static const String defaultApiBase = 'http://10.0.2.2:8080';
+
+  /// How often the gateway polls the API Server for pending messages.
+  static const Duration pollInterval = Duration(seconds: 10);
+
+  /// How often the device sends a heartbeat ping.
+  static const Duration pingInterval = Duration(minutes: 1);
+}