Apply Destination To Files Bulk

Bulk move-time access rewrite — one DB round-trip set for N files.

Same effect as calling PUT /files/{file_id}/share/apply-destination once per file, except the desired state is resolved ONCE (not per file) and the actual writes (file_shares/file_share_grants, timeline events) go through set_share_state_bulk/create_events_bulk instead of looping a single-row write per file. Per-file authorization/visibility still runs per file (cheap reads, and this is a security-sensitive check that must not be skipped) — a file that fails its own check is skipped rather than failing the whole batch, and reported back in failed_file_ids so the caller can surface a real error instead of failing silently.