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>

Home Assistant Plugin/custom_components/gsmnode/manifest.json

@@ -0,0 +1,13 @@
+{
+  "domain": "gsmnode",
+  "name": "gsmnode",
+  "version": "1.2.0",
+  "config_flow": true,
+  "documentation": "https://github.com/your-org/sms-gateway",
+  "issue_tracker": "https://github.com/your-org/sms-gateway/issues",
+  "dependencies": [],
+  "codeowners": [],
+  "requirements": [],
+  "integration_type": "service",
+  "iot_class": "local_polling"
+}