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/pages/TripPlannerPage.tsx

@@ -495,6 +495,7 @@ export default function TripPlannerPage(): React.ReactElement | null {
                 )}
                 <div style={{ flex: 1, overflow: 'hidden', display: 'flex', flexDirection: 'column', paddingLeft: 4 }}>
                   <PlacesSidebar
+                    tripId={tripId}
                     places={places}
                     categories={categories}
                     assignments={assignments}
@@ -604,7 +605,7 @@ export default function TripPlannerPage(): React.ReactElement | null {
                   <div style={{ flex: 1, overflow: 'auto' }}>
                     {mobileSidebarOpen === 'left'
                       ? <DayPlanSidebar tripId={tripId} trip={trip} days={days} places={places} categories={categories} assignments={assignments} selectedDayId={selectedDayId} selectedPlaceId={selectedPlaceId} selectedAssignmentId={selectedAssignmentId} onSelectDay={(id) => { handleSelectDay(id); setMobileSidebarOpen(null) }} onPlaceClick={handlePlaceClick} onReorder={handleReorder} onUpdateDayTitle={handleUpdateDayTitle} onAssignToDay={handleAssignToDay} onRouteCalculated={(r) => { if (r) { setRoute(r.coordinates); setRouteInfo({ distance: r.distanceText, duration: r.durationText }) } }} reservations={reservations} onAddReservation={(dayId) => { setEditingReservation(null); tripStore.setSelectedDay(dayId); setShowReservationModal(true); setMobileSidebarOpen(null) }} onDayDetail={(day) => { setShowDayDetail(day); setSelectedPlaceId(null); setSelectedAssignmentId(null); setMobileSidebarOpen(null) }} accommodations={tripAccommodations} onNavigateToFiles={() => { setMobileSidebarOpen(null); handleTabChange('dateien') }} />
-                      : <PlacesSidebar places={places} categories={categories} assignments={assignments} selectedDayId={selectedDayId} selectedPlaceId={selectedPlaceId} onPlaceClick={handlePlaceClick} onAddPlace={() => { setEditingPlace(null); setShowPlaceForm(true); setMobileSidebarOpen(null) }} onAssignToDay={handleAssignToDay} days={days} isMobile onCategoryFilterChange={setMapCategoryFilter} />
+                      : <PlacesSidebar tripId={tripId} places={places} categories={categories} assignments={assignments} selectedDayId={selectedDayId} selectedPlaceId={selectedPlaceId} onPlaceClick={handlePlaceClick} onAddPlace={() => { setEditingPlace(null); setShowPlaceForm(true); setMobileSidebarOpen(null) }} onAssignToDay={handleAssignToDay} days={days} isMobile onCategoryFilterChange={setMapCategoryFilter} />
                     }
                   </div>
                 </div>