feat: send song requests to Hermes via webhook

- Add Hermes webhook settings form in /admin/settings (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 POST the generated MusicGPT prompt back to /api/prompt/<id>
- Add test button, update README workflow, bump version to 0.9.0

templates/admin/request.html

@@ -473,8 +473,11 @@
       <div class="right">
         <!-- Generate Music Prompt -->
         <div class="section">
-          <h2>1. Generate & Save Music Prompt</h2>
+          <h2>1. Generate &amp; Save Music 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 MusicGPT prompt?')">🚀 Send to Hermes</button>
+          </form>
           <p class="copy-hint">Paste Hermes' Title, Style, and Lyrics directly into the fields below, then save or generate.</p>
 
           {% if req.musicgpt_error %}

templates/admin/settings.html

@@ -339,6 +339,37 @@
         </form>
       </div>
 
+      <!-- Hermes webhook integration -->
+      <div class="section">
+        <h2>Hermes Webhook</h2>
+        <p class="copy-hint">Push song request data to Hermes so it can generate a MusicGPT prompt automatically. The URL must include the route name (e.g. https://ntfy.hallsworth.ca/webhooks/trollgorithm-song-info). The secret is encrypted before storage.</p>
+        <form method="POST">
+          <input type="hidden" name="action" value="save_hermes_webhook">
+          <table class="meta-table">
+            <tr>
+              <td>Webhook URL</td>
+              <td><input type="text" id="hermes_webhook_url" name="hermes_webhook_url" value="{{ hermes_webhook.get('url', '') }}" placeholder="https://ntfy.hallsworth.ca/webhooks/trollgorithm-song-info"></td>
+            </tr>
+            <tr>
+              <td>HMAC Secret</td>
+              <td>
+                <input type="password" id="hermes_webhook_secret" name="hermes_webhook_secret" placeholder="{% if hermes_webhook.get('secret') %}Stored encrypted — type to replace{% else %}Enter secret{% endif %}">
+                <p class="copy-hint">From the Hermes webhook subscription. Leave blank to keep the existing stored secret.</p>
+              </td>
+            </tr>
+          </table>
+          <button type="submit">Save Hermes Webhook</button>
+        </form>
+
+        <hr style="border:none;border-top:1px solid var(--border);margin:1.5rem 0;">
+
+        <h3>Send Test Request</h3>
+        <form method="POST">
+          <input type="hidden" name="action" value="send_test_hermes_webhook">
+          <button type="submit">Send Test to Hermes</button>
+        </form>
+      </div>
+
       <!-- MusicGPT integration -->
       <div class="section">
         <h2>MusicGPT Integration</h2>