fix(errors): stop naming a flag this PR no longer has

`IngressBlockedError`'s docstring hint pointed at `--from-file`, which left this
branch with the rest of the migration flags. A refusal must not tell a user to
run something that does not exist.

Also records the judgement call on the human path: `site`/`--user` were required
by Typer before this work and are optional now (the claim path needs them
optional), so the human path rejects a missing `--user` with the friendly
message and exit 1 instead of Typer's "Missing option" and exit 2.
