Add partner SMS gateway via Gama SendQuick and document it.

Expose POST /public/sms/send with API key + domain allowlist for external backends like Balout, wire Meshkee OTP/message sends to Gama, and publish Partner SMS docs on /docs/website.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/website-api/index.html

@@ -77,6 +77,7 @@
       <a class="btn" href="/docs/website/openapi.json">OpenAPI JSON</a>
       <a class="btn secondary" href="/docs/website/Meshkee-Website-API.postman_collection.json">Download Postman</a>
       <a class="btn secondary" href="/docs/website/AI_PROMPT.md">AI prompt</a>
+      <a class="btn secondary" href="/docs/website/SMS.md">Partner SMS</a>
     </div>
 
     <h2>Base URL</h2>
@@ -104,6 +105,17 @@
       Postman → Import → Link → paste<br />
       <code>https://api.meshkee.com/docs/website/Meshkee-Website-API.postman_collection.json</code>
     </p>
+
+    <h2>Partner SMS gateway</h2>
+    <p>
+      External backends (e.g. Balout) can send transactional SMS through Meshkee → Gama.
+      Server-to-server only — API key per allowlisted domain. See
+      <a href="/docs/website/SMS.md">SMS.md</a>.
+    </p>
+    <div class="panel">
+      <p style="margin:0"><code>POST /api/v1/public/sms/send</code></p>
+      <p style="margin:0.5rem 0 0">Header <code>X-Api-Key</code> + body <code>{ domain, to, message }</code></p>
+    </div>
   </main>
 </body>
 </html>