XY-704: Lane control P1: implement broad CLI/API steer for active turns

[yvette-carlisle]

Summary

• Add decodex lane steer and POST /api/lane-steer with expectedTurnId precondition and broad operator text input.
• Route active app-server attempts through the local run-control steer channel to turn/steer, with accepted/rejected/delivery audit records and distinct steer failure classes.
• Surface compact steer status/evidence without raw operator text, and update lane-control/app-server docs plus Decodex skills.

Verification

• cargo make fmt
• cargo make lint-fix
• cargo make test (929 passed, 1 skipped)
• cargo run -q -p decodex --bin decodex -- lane steer --help
• git diff --check