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/configuration.example.yaml

@@ -0,0 +1,49 @@
+# RECOMMENDED: add this integration from the UI instead
+# (Settings -> Devices & Services -> Add Integration -> gsmnode).
+# The blocks below are only for the OPTIONAL legacy `notify.gsmnode`
+# YAML service and for receiving incoming SMS via a webhook.
+
+# --- Optional: legacy notify.gsmnode YAML service ---------------------
+notify:
+  - platform: gsmnode
+    name: gsmnode                 # service becomes notify.gsmnode
+    api_base: http://10.2.1.10:8080   # the gsmnode API Server (reachable from HA)
+    email: !secret gsmnode_email
+    password: !secret gsmnode_password
+    device_id: my-phone               # optional: pin to a specific device
+
+# secrets.yaml:
+#   gsmnode_email: you@example.com
+#   gsmnode_password: your-password
+
+# --- Usage ----------------------------------------------------------------
+# Send an SMS:
+#   service: notify.gsmnode
+#   data: { message: "Hello", target: ["+15551234567"] }
+#
+# Place a phone call (gateway phone dials the number; message is ignored):
+#   service: notify.gsmnode
+#   data: { message: "", target: ["+15551234567"], data: { type: call } }
+
+# --- Optional: receive incoming SMS as Home Assistant events ---------------
+# The API Server can POST the `sms:received` webhook to a HA webhook trigger.
+#
+# 1. Create an automation with a webhook trigger (gives you a webhook_id):
+#
+# automation:
+#   - alias: "gsmnode - incoming SMS"
+#     trigger:
+#       - platform: webhook
+#         webhook_id: gsmnode_incoming
+#         allowed_methods: [POST]
+#         local_only: true
+#     action:
+#       - service: persistent_notification.create
+#         data:
+#           title: "SMS from {{ trigger.json.payload.phone_number }}"
+#           message: "{{ trigger.json.payload.message }}"
+#
+# 2. Register the webhook with the API Server (one-time), pointing at:
+#      http://<home-assistant>:8123/api/webhook/gsmnode_incoming
+#    e.g. via the Web App "Webhooks" page or:
+#      POST /api/webhooks  {"event":"sms:received","url":"<that url>"}