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>

API Server/panel/vite.config.js

@@ -0,0 +1,20 @@
+import { defineConfig } from "vite";
+import vue from "@vitejs/plugin-vue";
+import tailwindcss from "@tailwindcss/vite";
+
+// Builds into internal/api/dist, which the Go server embeds via go:embed
+// and serves at the server root.
+export default defineConfig({
+  plugins: [vue(), tailwindcss()],
+  build: {
+    outDir: "../internal/api/dist",
+    emptyOutDir: true,
+  },
+  server: {
+    port: 5174,
+    proxy: {
+      // Dev-mode proxy to a locally running API Server.
+      "/api": "http://localhost:8080",
+    },
+  },
+});