file.move unifies: any kind, no policy, move_directory retires #620

Feature: #616 · Phase 4 of any-entry-claims.md.

1. file.move(source Entry, destination_path) — moveEntry's shared core is already kind-agnostic, so the two typed fronts collapse onto it. Moving a symbolic link works again (the regression from file.discover and file.resolve; kind-honest activation #611).
2. on_missing is removed from move. Moving something that is gone accomplishes nothing, so a missing source fails — under Stop-by-default that is a pre-flight verdict at the starting line rather than a dispatch error. The tolerance was also unsound on a producer: the ignore path returned a nil product, handing downstream consumers a nil promise — the pathology that had Skip dropped from MissingResourcePolicy (feat(op): the consumed-Gone guard with the narrated verdict; Skip is dropped — phase 3's docket completes #605).
3. file.move_directory retires (removed, not deprecated); writ migrate's layer registration reverts to file.move.

Acceptance: moving a symbolic link (the link moves, its target is untouched), moving a directory through the unified move, and the missing-source verdict landing at pre-flight rather than dispatch.