**Acceptance criteria:** - [ ] An "Export GeoJSON" button in the top nav calls `GET /api/export/geojson` - [ ] The response is downloaded as `festival-map-YYYY-MM-DD.geojson` - [ ] No new browser tab is opened — download uses a temporary `<a>` element - [ ] The button shows a spinner while the request is in flight - [ ] A success toast confirms the export; API errors are shown in an error toast
Acceptance criteria:
GET /api/export/geojsonfestival-map-YYYY-MM-DD.geojson<a>element