feat(collections): import a whole trip's places into a list (#1903)

* feat(collections): preview which of a trip's places a list already holds

The bulk import endpoint has been there since the select-mode copy, but nothing
calls it and it only reports duplicates after the fact. A dialog needs the verdict
up front, so /:id/importable/:tripId returns the trip's places with the duplicate
check the import itself applies, plus whether any day holds the place.

* feat(collections): import a whole trip's places into a list

Two steps: pick a trip, then tick its places. Places already on the list are
greyed out and unpickable, and the ones no day holds start selected — those are
the plans a trip left behind, which is the reason to import at all. Sorted so a
mostly-saved trip reads as the two that are left rather than a wall of grey.

* feat(collections): reach the trip import from the filter row and an empty list

* i18n(collections): translate the trip import into all locales

* fix(collections): stop the label dialog's buttons wrapping mid-word

Three actions in a max-w-sm footer wrapped into two lines each. The assign
button also painted white text on the accent, which disappears on a light one.

* docs(collections): document the trip import

client/src/api/collections.ts

@@ -9,6 +9,7 @@ import type {
   CollectionUpdateRequest,
   CollectionSavePlaceRequest,
   CollectionSaveFromTripRequest,
+  CollectionImportablesResponse,
   CollectionPlaceUpdateRequest,
   CollectionCopyToTripRequest,
   CollectionInviteRequest,
@@ -68,6 +69,8 @@ export const collectionsApi = {
     ax.post(`${base}/places/from-trip`, body satisfies CollectionSaveFromTripRequest).then((r: AxiosResponse) => r.data),
   saveFromTripMany: (collectionId: number, tripId: number, placeIds: number[], force?: boolean): Promise<{ copied: number; skipped: { id: number; name: string }[] }> =>
     ax.post(`${base}/places/from-trip-many`, { collection_id: collectionId, source_trip_id: tripId, source_place_ids: placeIds, force }).then((r: AxiosResponse) => r.data),
+  importable: (collectionId: number, tripId: number): Promise<CollectionImportablesResponse> =>
+    ax.get(`${base}/${collectionId}/importable/${tripId}`).then((r: AxiosResponse) => r.data),
   updatePlace: (pid: number, body: CollectionPlaceUpdateRequest): Promise<CollectionPlace> =>
     ax.patch(`${base}/places/${pid}`, body satisfies CollectionPlaceUpdateRequest).then((r: AxiosResponse) => r.data),
   uploadPlaceImage: (pid: number, formData: FormData): Promise<CollectionPlace> =>