Post the triage "starting work" ack deterministically

[imaustink]

Summary

Fixes: a labeled issue/PR triage run just launched an AgentRun Job in the cluster with no acknowledgement comment posted on the ticket at all.

relayAndReply (apps/integration-gateway/src/server.ts) only ever posts an upfront comment when a genuine remote-control-url progress event arrives from the delegated agent (onRemoteControlUrl, from commit c49a533). That was a deliberate call at the time — it stopped a stale session-page link from appearing on every run regardless of whether Remote Control actually worked. But the flip side: if that event never arrives (Remote Control not configured for the Agent, the CLI never hands back a session, or the agent fails before reaching that point), no comment posts at all, even though the run visibly launched a Job — which is exactly what we just observed against the live cluster.

Fix

orchestratorClient.invoke's onRunning callback already exists for precisely this case: it fires deterministically off this gateway's own poll of the turn's status (the moment it's genuinely running, past any identity-link pre-flight) — independent of anything the delegated agent itself does or doesn't emit. It was already threaded through runTurn but relayAndReply passed undefined for it.

Restored it as a plain, deterministic ack: "🤖 Starting work on this now." — no link, so nothing about it depends on Remote Control succeeding. The Remote Control URL, when one does arrive, now posts as its own separate follow-up comment ("🤖 Watch live or take over the session here: <url>") rather than being combined into one comment as before — the two signals are independent and shouldn't block on each other.

Test plan

• Updated/added server.test.ts cases:
  • the default (no Remote Control URL ever arrives) case now expects the deterministic ack + final result (2 comments), not silence.
  • the Remote Control URL case now expects the ack and the URL as separate comments.
  • the deferred-ack/auto-resume suite's resumed-turn cases now expect the ack between the auth prompt and the final result (3 comments total).
• npx vitest run in apps/integration-gateway — 299/299 passing.
• npx tsc --noEmit in apps/integration-gateway — clean.