Add delete with confirmation for trips and dashcam

- Confirmation modal in server base.html (window.confirmDelete promise helper)
- Trip delete: trash button in Replay column (server-only via data-deletable on
  trip-list div), DELETE /api/v1/portal/trip/<id>, removes computed trip only
  (raw tracking_points kept)
- Dashcam delete: trash button next to download, DELETE /api/v1/portal/dashcam/<id>,
  removes from DB + disk (best-effort file removal)
- history.js: delete button gated on data-deletable='1' attribute; click handler
  intercepts before replay logic
- db.py: delete_trip(), delete_dashcam_file() helpers

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

server/templates/history.html

@@ -34,7 +34,8 @@
                         {"key": "action", "label": "", "sortable": false, "class": "d-none d-sm-table-cell"}
                     ],
                     "No trips detected",
-                    "Trips appear once the Pi has uploaded tracking data."
+                    "Trips appear once the Pi has uploaded tracking data.",
+                    true
                 ) }}
             </div>
         </div>