fix review findings: whenIdle() is observation, not the teardown await

Codex's confirmation pass found the teardown-framing error went deeper than the
three prose spots already fixed: the whenIdle() JSDoc itself (and its mirrors)
claimed "the quiescence signal a teardown awaits ... a lifecycle owner disposes
the agent through its AgentHandle which ... awaits THIS". The disposer does not
call whenIdle() — it does `stop(); await agent.done` directly
(packages/core/agent-loop/src/index.ts:271). whenIdle() is the NON-OWNER
observation hook; owner teardown awaits the loop-exit promise (done) through
AgentHandle.dispose(). Reframe every copy accordingly:

- packages/core/agent/src/types.ts: the Agent.whenIdle() contract JSDoc.
- packages/core/agent-loop/src/agent.ts: the impl JSDoc.
- packages/core/agent/README.md and docs/core-data-structures/core.md (the
  type-equiv mirror of the types.ts JSDoc — re-copied verbatim).
- docs/rfc/proposed/feature/2026-06-14-acp-agent-client-protocol.md:40 and :70:
  owner teardown via AgentHandle.dispose(); a non-owner observing quiescence
  uses the interface-level agent.whenIdle(), not hand-rolled agent/status.
- Regenerate the cordis catalog (whenIdle source line moved).

packages/core/agent-loop/src/agent.ts

@@ -228,8 +228,10 @@ export class ReactLoopAgent implements Agent {
    * internal waiter (see {@link idleWaiters}) released on the next
    * running→idle/disposed transition, resolving on `idle` directly (the turn
    * fully ended) or chaining {@link done} on `disposed` (wait for the loop to
-   * actually exit). Implements the {@link Agent.whenIdle} contract used by
-   * teardown (handle disposal aborts in-flight work, then awaits `whenIdle()`).
+   * actually exit). Implements the {@link Agent.whenIdle} contract: a non-owner
+   * quiescence-observation hook, distinct from teardown (a lifecycle owner stops
+   * and unregisters via `AgentHandle.dispose()`, which awaits {@link done}
+   * directly, not through this).
    */
   whenIdle(): Promise<void> {
     if (this._status === 'disposed') return this.done