fix review findings: drop the false "closing ACP connection" whenIdle() example

The whenIdle() JSDoc cited "a closing ACP connection" as a non-owner that
awaits whenIdle(). That is false against the code: ACP OWNS its agent handles
and tears them down via rec.dispose()/handle.dispose() (quiesce() at
packages/ui/acp/src/index.ts:666-686), never whenIdle(). The only whenIdle()
consumers are tests (acp dispose/turns/edges specs, agent specs) — which is
genuinely why the primitive stays (a test harness programs against the seam),
but the contract doc must not claim a production ACP path uses it.

Replace the parenthetical with truthful non-owning observers (a test awaiting a
turn to settle, a monitor) and state explicitly that an OWNER does not need
whenIdle() because AgentHandle.dispose() already awaits the loop-exit promise.

- packages/core/agent/src/types.ts: the Agent.whenIdle() contract JSDoc.
- docs/core-data-structures/core.md: the type-equiv mirror (re-copied verbatim).
- Regenerate the cordis catalog (whenIdle source line shifted).

docs/core-data-structures/core.md

@@ -255,12 +255,13 @@ interface Agent {
    * Resolve once the agent has reached quiescence after settling out of
    * `running`, or immediately if it is already idle with no queued work. A
    * non-owner's quiescence-observation hook: a consumer that does NOT own the
-   * agent's lifecycle (a closing ACP connection, a UI plugin) awaits this to
-   * proceed only after queued/running work has fully stopped, rather than
-   * returning while the driver is still streaming or about to start a queued
-   * turn. It does NOT tear the agent down — a lifecycle owner stops and
-   * unregisters the agent through its `AgentHandle.dispose()` (which awaits the
-   * loop-exit promise directly), separate from this.
+   * agent's lifecycle awaits this to proceed only after queued/running work has
+   * fully stopped, rather than returning while the driver is still streaming or
+   * about to start a queued turn — without itself tearing the agent down. (A
+   * lifecycle OWNER does not need it: `AgentHandle.dispose()` already awaits the
+   * loop-exit promise directly as part of stopping and unregistering. So this is
+   * for a non-owning observer — e.g. a test awaiting a turn to settle, or a
+   * monitor — that wants the settle signal but must not dispose the agent.)
    *
    * "Quiescence", not merely "status changed": a disposed agent emits
    * `agent/status('disposed')` from inside its disposer, BEFORE the driver loop