Implement manual federation sync and peer status surface

[enricopiovesan]

Summary

Implement the operator surface for trusted peer listing, manual sync execution, and sync-status reporting across federated Traverse instances.

Depends on

• Implement multi-instance registry federation #213

Definition of Done

• A trusted peer can be listed from the supported operator surface.
• A manual sync can be triggered and returns a structured sync-session result.
• Sync status and last-sync evidence are visible after sync completes.
• The implementation is covered by deterministic tests or fixture-driven validation.

[enricopiovesan]

Implementation started in PR #247. Validation: cargo test -p traverse-cli; bash scripts/ci/repository_checks.sh.

[enricopiovesan]

Closing this now: the manual federation sync and peer status surface landed in PR #247.