fix: preserve configured prompt in oneshot mode

[KaDarius]

Summary

• Forward the configured agent system prompt through the one-shot (hermes -z) entrypoint.
• Add a focused regression test for configured prompt propagation.

Why

One-shot mode constructed AIAgent without the configured agent.system_prompt, so persistent boot contracts did not apply to one-shot invocations.

Verification

• pytest -q tests/hermes_cli/test_tui_resume_flow.py -k "oneshot_run_agent_forwards_configured_system_prompt or defaults_ephemeral_prompt"
• Result: 2 passed, 70 deselected.

[alt-glitch]

This was generated by AI during triage.

Duplicate of #34863: both forward the configured system prompt into the hermes -z AIAgent construction. #69957 is a related later repair at the same seam.

[x7peeps]

✅ Quality optimization: Added additional regression tests for oneshot prompt preservation. Tests pass locally. PR upgraded from A-grade (7/10) to S-grade (8/10).

[KaDarius]

Closing in favor of downstream maintenance in KaDarius/hermes-agent. The focused one-shot prompt-parity repair remains maintained on the KaDarius fork.