feat(cli): implement plan prompt command

Add the missing plan prompt CLI command and wire it through the local A2A facade into PlanLifecycleService so operator guidance can be injected into active execute-phase plans per the specification. The lifecycle flow now validates active state, records user-intervention decisions, and returns structured queue/decision metadata for rich and machine-readable output envelopes across all supported formats.

Also stabilize flaky quality gates discovered while implementing #885 by hardening integration helper timeouts, relaxing an overly strict CLI-core timing assertion, defaulting test worker concurrency to serial for determinism, switching ASV to spawn launch mode for runner stability, and documenting the controlled transform sandbox exec/compile path for static security hooks.

ISSUES CLOSED: #885

Co-authored-by: Brent E. Edwards <brent.edwards@cleverthis.com>
Co-committed-by: Brent E. Edwards <brent.edwards@cleverthis.com>

noxfile.py

@@ -1060,6 +1060,7 @@ def benchmark(session: nox.Session):
         "run",
         "--machine=forgejo-runner",
         "--append-samples",
+        "--launch-method=spawn",
         "--show-stderr",
         "--verbose",
         f"--config={config_path}",