Check a claim’s proof

Checks the claim’s proof by its method: the token on the page the entry lists (url, fetched once, through the same guard as every fetch the site makes), in a DNS TXT record (dns), or your account’s verified email being an address the entry lists or a role address (admin@, administrator@, webmaster@, hostmaster@, postmaster@) at a domain it lists (email). Found, the entry is claimed at once: it is yours, and the Wikidata sync stops changing it (unless it is locked to admins). Found on an entry someone else holds: 202 {"review":"transfer"}, and an administrator decides the transfer in the review queue; nothing changes until then. Any other address at a domain the entry lists is not proof, but evidence: 202 {"review":"domain"}, for an administrator to decide. Either way the claimant is emailed the decision, and checking again answers the same 202. Not found: 422, with what was seen, and the claim stays open to check again until it expires. Its submitter may check it, and so may a reviewer.