Implement session.list_jobs / session.jobs

[nficano]

ARCP v1.1 §6.6 adds session.list_jobs (request) and session.jobs (response). Not in PHP SDK.

Steps:

1. Add ListJobs and Jobs message classes under src/Messages/Session/
2. Register them in the message catalog / serializer
3. Implement runtime handler returning current job list with cursored pagination
4. Add client API: $client->listJobs()
5. Add a samples/list_jobs/ runnable demo
6. Add unit + integration tests

Reference: spec §6.6, §13.3.

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Audit reference: ARCP SDK Audit v1.1 (2026-05-19)