feat(import): the archive's portrait in the import preview, and what an import applies

[aleskiontherun]

The import preview's check-in section now carries the archive's portrait beside the account's, the archive's chosen and "Keep mine" one click away, and the section shows for an archive carrying a portrait and no check-in fact. The apply sends the choice as the portrait field with the account_sha256 the preview showed, on keep as on take, since the API requires the key; with nothing offered no field is sent and the account keeps its portrait. A stored portrait is noted check_in_detail_written, which already re-reads the signed-in user, so the portrait slot and "Adjust" pick up the new digests with no refresh of this change's own. portrait_kept joins the note codes as information. The dropzone, the export card's archive row, the README and the privacy page (§2.1's pictures paragraph and §2.3's photo GPS) now say an import offers the archive's portrait and the check-in details rather than restoring them silently.

Verified with npm run ci (lint, type-check, the full vitest suite, build) and new render and unit tests over the row, the choice and the apply's form data.

🤖 Generated with Claude Code