List, update or unlist a site

Makes the API read <site>/.well-known/x402 itself. The site is listed only if that document offers an x402 exact payment to the P2Flux vault of the wallet it names, on this network; it is unlisted when the document is gone, no longer verifies, or says directory: false. Whoever runs the site controls its listing - nobody else can add or remove it. site must be an https address on the default port with a public host name. A site is refreshed at most 10 times a day.