New 'sync at attach' flow pulls a peer's files as soon as it joins a session

What

When a peer attaches to a cloud or directory-sync session, Claude Code can now offer to sync files right away instead of waiting for the normal push/pull cycle:

• If the peer advertises the sync_at_attach capability and a local check passes, the new flow calls the peer's attachOffer()/pullPoint() to pull the peer's files into the local session before the usual sync cycle runs.
• The local check requires the account gate tengu_violin_soundpost and the broader remote-tools gate tengu_violin_wood to both be enabled.
• The flow emits the telemetry event tengu_dir_sync_attach_offer and counters under ccr_dir_sync_attach.

Why

This lets a newly attached peer get an up-to-date copy of files sooner, rather than waiting for the regular sync cycle, while keeping the behavior behind capability negotiation and account gates so it only activates where supported and enabled.