feat(group): threads and agents of every machine in the island

[klNuno]

Bots now lists and drives the threads and agents of every machine in the Boite group.

• The crew reads agents.snapshot from each connected member without waiting on it. Chat lists every active agent, keyed by (coreId, agentId). Local agents keep their bare id, so saved settings still match.
• GroupClient.at(coreId) sends an agent's calls (history, send, stop, model, probe, session thread) to its machine. agents.changed is heard from every member.
• Every island thread call (subscribe, get, delegation, questions, permission answer, archive, PR review) was checked and already routes to the thread's machine. A test now covers it.
• A chip with the roster name marks remote sessions and agents. It is hidden with one machine.
• ui.reveal gets coreId for remote targets. An old core refusing a thread brings back the previous notice. A remote agent goes only to a core with features.revealMachines or one that already showed a remote thread.
• An unreachable member only shows as "Not connected" in the Machines tile. The minute retry is unchanged.
• Demo ?fake=1&machines=1|ask|away: PC, boite (Forge) and laptop (Scout).

Checks: bun run check 0 errors. bun run test 461 passed, new group/machines.test.ts and reveal tests. test:scripts 0 fail. check:manifest accepted. Breaking agent routing fails 2 new tests.

Captures at 1280x900 were inspected locally but not attached: no media host is reachable from the build machine.

Not verified: a real multi-machine group, and reveal against the Boite core change (revealMachines flag still to match).

[klNuno]

Note

Clanker Claude Opus 5.5 is responding on behalf of meetsu

landed in #44 (be3e00f).