[feature request] Static link to a specific version of a site

_[ Edit: This was not initially well thought out. To keep the record of the conversation intact, I have kept the rest of this post as I first posted it; for those just joining us, the actual feature request is [further downthread](#issuecomment-286954890). ]_

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It would be nice to be able to have static (immutable, non-updatable) zites. There are many cases where immutability is a positive feature from a security perspective, especially from the perspective of auditability.

A static zite would differ from e.g. an IPFS site in that it could access the ZeroFrame API, and therefore act as a client for a networked protocol, whereas an IPFS site is purely read-only. Through the API, static zites could have mutable state; only the code would be immutable, not the data.

Start with the further-downthread feature request referenced in the issue, especially comment 286954890, rather than the original proposal. Identify the affected site-version and ZeroFrame API entry points from that discussion; the issue does not name files or tests, and its acceptance criteria are not available here.

索引モデルが issue の本文から書いたものです。