fix: validate a query host at the one point a query is admitted

THE FOURTH PROPERTY was breached through the domain branch of worklist().
The url branch is cleaned by _host_of, which uses urlsplit().hostname,
and the domain branch did only value.strip(".").lower(). rdap.query_domain
then interpolates that value into the fetch URL with no quoting.

parse._domain_of takes everything after the @ of a From, Sender or
Reply-To addr-spec, and email.utils.parseaddr permits /, ?, # and %
there, so the whole shape is attacker-controlled through a header they
own. A From of `Bank <phish@victim%40example.org.invalid>` sent the
recipient's own address to a registry, which is precisely the identity
disclosure the property exists to prevent, reaching a third party.
`a/../../x.invalid` escaped the /domain/ endpoint altogether, and query,
fragment and space values all reached the wire.

Fixed at the SINGLE admission point rather than in the offending branch,
because per-branch validation is what failed here: one branch was
cleaned, the next was written without it. is_queryable() now guards
worklist()'s add(), so domain, url and any future branch pass through it.

A rejected value is not dropped. It keeps an entry with an empty abuse
list and an error saying it was never queried, following the rule
suspect_path_segments already sets: flagged and visible to the user
during review, because silent was the bug.

A non-ASCII host is refused rather than encoded to punycode. Guessing the
encoding of an attacker-supplied name is a query that cannot be
justified, and the ceiling is noted in a ponytail comment.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wrfqr2xqQfhtXCscU7zrdz

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