feat: send song requests to Hermes via webhook

- Add Hermes webhook platform support on ntfy.hallsworth.ca
- Add /admin/settings form to configure webhook URL + HMAC secret
- Add /admin/request/<id>/send-to-hermes action
- POST request data to Hermes with V2 HMAC signature and callback URL
- Hermes can reply via chat or POST the Suno prompt back to /api/prompt/<id>
- Add test button, update README, bump version to 0.7.0

templates/admin/request.html

@@ -326,6 +326,9 @@
         <div class="section">
           <h2>1. Generate &amp; Save Suno Prompt</h2>
           <button type="button" onclick="copyPromptForHermes()">Copy customer info for Hermes</button>
+          <form method="POST" action="{{ url_for('send_to_hermes', rid=req.id) }}" style="display:inline">
+            <button type="submit" onclick="return confirm('Send this request to Hermes to generate a Suno prompt?')">🚀 Send to Hermes</button>
+          </form>
           <p class="copy-hint">Paste Hermes' Title, Style, and Lyrics directly into the fields below, then save.</p>
 
           <form method="POST">