feat: bulk import for packing lists + complete i18n sync — closes #133

Packing list bulk import:
- Import button in packing list header opens a modal
- Paste items or load CSV/TXT file
- Format: Category, Name, Weight (g), Bag, checked/unchecked
- Bags are auto-created if they don't exist
- Server endpoint POST /packing/import with transaction

i18n sync:
- Added all missing translation keys to fr, es, nl, ru, zh, ar
- All 8 language files now have matching key sets
- Includes memories, vacay weekdays, packing import, settlement,
  GPX import, blur booking codes, transport timeline keys

client/src/api/client.ts

@@ -112,6 +112,7 @@ export const assignmentsApi = {
 export const packingApi = {
   list: (tripId: number | string) => apiClient.get(`/trips/${tripId}/packing`).then(r => r.data),
   create: (tripId: number | string, data: Record<string, unknown>) => apiClient.post(`/trips/${tripId}/packing`, data).then(r => r.data),
+  bulkImport: (tripId: number | string, items: { name: string; category?: string; quantity?: number }[]) => apiClient.post(`/trips/${tripId}/packing/import`, { items }).then(r => r.data),
   update: (tripId: number | string, id: number, data: Record<string, unknown>) => apiClient.put(`/trips/${tripId}/packing/${id}`, data).then(r => r.data),
   delete: (tripId: number | string, id: number) => apiClient.delete(`/trips/${tripId}/packing/${id}`).then(r => r.data),
   reorder: (tripId: number | string, orderedIds: number[]) => apiClient.put(`/trips/${tripId}/packing/reorder`, { orderedIds }).then(r => r.data),