feat: GPX file import for places — closes #98

Upload a GPX file to automatically create places from waypoints.
Supports <wpt>, <rtept>, and <trkpt> elements with CDATA handling.
Handles lat/lon in any attribute order. Track-only files import
start and end points with the track name.

- New server endpoint POST /places/import/gpx
- Import GPX button in PlacesSidebar below Add Place
- i18n keys for DE and EN

client/src/api/client.ts

@@ -91,6 +91,10 @@ export const placesApi = {
   update: (tripId: number | string, id: number | string, data: Record<string, unknown>) => apiClient.put(`/trips/${tripId}/places/${id}`, data).then(r => r.data),
   delete: (tripId: number | string, id: number | string) => apiClient.delete(`/trips/${tripId}/places/${id}`).then(r => r.data),
   searchImage: (tripId: number | string, id: number | string) => apiClient.get(`/trips/${tripId}/places/${id}/image`).then(r => r.data),
+  importGpx: (tripId: number | string, file: File) => {
+    const fd = new FormData(); fd.append('file', file)
+    return apiClient.post(`/trips/${tripId}/places/import/gpx`, fd, { headers: { 'Content-Type': 'multipart/form-data' } }).then(r => r.data)
+  },
 }
 
 export const assignmentsApi = {