feat: add server-side device deletion

- add portal API and UI action to delete non-default devices
- protect the configured portal default device from deletion
- document that trip/history pages still scope to the single DEVICE_NAME

Co-authored-by: Copilot <[email protected]>

server/templates/device_settings.html

@@ -57,6 +57,9 @@
                     <button class="btn btn-outline-primary btn-sm" id="request-sync-button" type="button" disabled>
                         <i class="fas fa-rotate me-1"></i>Request sync
                     </button>
+                    <button class="btn btn-outline-danger btn-sm" id="delete-device-button" type="button" disabled>
+                        <i class="fas fa-trash-alt me-1"></i>Delete device
+                    </button>
                 </div>
             </div>
             <div class="card-body">
@@ -144,6 +147,7 @@
                     <li><strong>Request sync</strong> means “fetch this config on the Pi's next online contact”.</li>
                     <li>The car can still be offline; the remote server cannot push directly into it.</li>
                     <li>Use the Pi's local <strong>Sync now</strong> button for immediate pull attempts.</li>
+                    <li><strong>Delete device</strong> removes that device row and cascades its trips, tracking logs, and dashcam files from the server.</li>
                 </ul>
             </div>
         </div>