cli: reconcile peer-management UX

[fosskar]

Both mechanisms are live: namespace tickets (ssync ticket / ssync join <ticket>) do pairing, while the config peers node-id list feeds sync_with_peers resync via discovery. Decide the user-facing story and align docs.

Likely direction: tickets stay the pairing UX, peers becomes plumbing that join populates, plus ssync peer list/remove for hygiene.

Refs: TODO.md Open #5, docs/pairing.md.

[fosskar]

Superseded by #23, which owns the whole peer-management story now (membership lifecycle + ticket/peers-list reconciliation + ssync peer list/remove hygiene — folded in there).