fix: [ENG-3025] surface companion errors in text-mode + sync doc skeleton

Real regression caught in third-round review: when the previous fix
moved --delete-response-file cleanup failures from `warnings[]` to
`errors[]`, the text-mode emitter's `done` branch was left iterating
`warnings[]` only. JSON consumers saw the new `errors[0].kind` cleanly,
but `--format text` users with a successful curate + failed cleanup saw
`✓ Curated to ...` and nothing else — the cleanup failure vanished.

Fix the emitter to iterate companion `errors[]` on the `done` branch
too, prefixed with `⚠` to match the warnings convention. Same
"non-fatal companion" semantics the docs already describe.

Plus two doc lines tracking the new `done`-with-errors[] shape:

- JSON-skeleton comment for `errors[]` now lists the three valid
  placements (correct-html, failed, done-with-companion).
- Status-values table's `done` row notes the companion-errors case
  with a "treat as success; surface but don't abandon" hint so a
  contract author reading top-of-doc material doesn't assume any
  non-empty `errors[]` means failure.

Interactive verification: chmod-555 parent directory → text-mode
emits "✓ Curated to ..." plus "⚠ response-file-delete-error: ..."
on the next line.