feat: retain historical site versions by pinning published IPFS CIDs

[akhileshthite]

Currently, when we publish an updated version of a site to IPFS, only the new root CID is pinned—and the previous versions are immediately eligible for garbage collection. As a result, there’s no way to roll back to or audit any past state of the site once it’s been superseded.

Problem:

• Old site versions become inaccessible after publishing a new update.

Proposed Solution:

• Pin each published root CID in addition to the latest one (e.g. store them in a simple key-value index).
• Retention & unpublish policies:
  • Implement a retention policy (e.g. “keep last N versions” or “keep versions for X days”).
  • Selective unpublish: allow removal of specific CIDs or files from history and ensure they are garbage-collected.
• Support external pinning services: Introduce optional integrations with external pinning services like Pinata to offload archival storage and improve content availability across nodes.

[fauno]

@akhileshthite please make sure that a removed file is garbage collected, we'd want to be able to remove files from history when someone wants to unpublish something.