Multisig support

future enhancement. When publishing becomes popular, more security should be allowed at the site key level in the form of multisig or scriptsig of some type.

The issue names no files, tests, or entry points and only proposes multisig or scriptsig for site keys. Start by locating site-key publishing and the existing key or signature handling, then establish the intended security model and acceptance criteria. Done requires an agreed design, implementation scope, and tests for the chosen approach.

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