Add SMTP test email button and recipient field on settings page

templates/admin/settings.html

@@ -266,6 +266,16 @@
           </table>
           <button type="submit">Save Email Settings</button>
         </form>
+
+        <hr style="border:none;border-top:1px solid var(--border);margin:1.5rem 0;">
+
+        <h3>Send Test Email</h3>
+        <form method="POST">
+          <input type="hidden" name="action" value="send_test_email">
+          <label for="test_email_address">Test recipient address</label>
+          <input type="email" id="test_email_address" name="test_email_address" placeholder="you@example.com" required>
+          <button type="submit">Send Test Email</button>
+        </form>
       </div>
 
       <!-- MP3 metadata defaults -->