refactor(ingress): cut the wait loop and the file readers from the claim flow

The claim handoff is the feature: an agent that must not hold a secret asks for
the entry, prints a code, and the human fills it. Everything else this module
grew was a second feature riding on it:

- `wait_for_fill` / `parse_duration` / the poll loop and exit code 3 — the agent
  can run `psamvault pending` on its next turn, and a claim cannot be lost by
  not waiting because it lives on disk until its TTL.
- the file readers (`read_secret_from_file`, `read_env_secret`, the `.env`
  parser, `remove_env_line`) — "move a secret that is already a file into the
  vault" does not make the agent blind: a process that can read the file can
  already `cat` it.
- the filled-claim history (`mark_filled`, `filled_seconds_ago`).

`complete_claim` now deletes the record instead of marking it filled, so the
code cannot be replayed and there is no archive to leak.
