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/pubspec.yaml

@@ -0,0 +1,31 @@
+name: sms_gateway_phone
+description: gsmnode phone client — turns an Android phone into an SMS gateway controlled via the API Server.
+publish_to: "none"
+version: 1.0.0+1
+
+environment:
+  sdk: ">=3.4.0 <4.0.0"
+
+dependencies:
+  flutter:
+    sdk: flutter
+  http: ^1.2.2
+  shared_preferences: ^2.3.2
+  permission_handler: ^11.3.1
+  google_fonts: ^8.1.0
+
+dev_dependencies:
+  flutter_lints: ^4.0.0
+  flutter_launcher_icons: ^0.14.1
+
+flutter:
+  uses-material-design: true
+
+# App launcher icons — generated from the gsmnode design-system app icon.
+# Regenerate with: dart run flutter_launcher_icons
+flutter_launcher_icons:
+  android: true
+  image_path: "assets/icon/app-icon.png"
+  min_sdk_android: 21
+  adaptive_icon_background: "#2E9E6B"
+  adaptive_icon_foreground: "assets/icon/adaptive-foreground.png"