Support Multiple Values of Vouch

Vouch, as it stands, encourages the use of a single string to be the sole determiner if the Webmention’s target is to be accepted. Expanding it to allow a list of values gives the sender another chance at getting approved and the recipient more options to handle verifications.

(Originally published at: https://v2.jacky.wtf/post/dac422fc-efca-4c0e-a989-18007e9a4ee9)

Start with the Vouch specification and the linked original post; identify how a single-string value is currently defined for Webmention target acceptance. Document the list semantics and acceptance behavior, then verify the specification consistently describes sender and recipient handling.

Written by the indexing model from the issue text.