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/services.yaml

@@ -0,0 +1,53 @@
+send_sms:
+  name: Send SMS
+  description: Send an SMS through the gateway.
+  fields:
+    phone_numbers:
+      name: Phone numbers
+      description: One or more recipient phone numbers.
+      required: true
+      example: '["+15551234567"]'
+      selector:
+        text:
+          multiple: true
+    message:
+      name: Message
+      description: The text to send.
+      required: true
+      example: Hello from Home Assistant
+      selector:
+        text:
+          multiline: true
+    device_id:
+      name: Device
+      description: Device to send from (defaults to the configured / most recent device).
+      example: my-phone
+      selector:
+        text:
+    sim_number:
+      name: SIM number
+      description: Which SIM to use on a dual-SIM phone.
+      example: 1
+      selector:
+        number:
+          min: 1
+          max: 4
+          mode: box
+
+call:
+  name: Place call
+  description: Tell a gateway device to place an outbound phone call.
+  fields:
+    phone_number:
+      name: Phone number
+      description: The number to call.
+      required: true
+      example: "+15551234567"
+      selector:
+        text:
+    device_id:
+      name: Device
+      description: Device to call from (defaults to the configured / most recent device).
+      example: my-phone
+      selector:
+        text: