docs: add HIL bring-up checklist + capture 2026-06-16 SIL operational lessons

[Copilot]

This PR captures operational knowledge re-learned during the 2026-06-16 (Denver/MDT) SIL/HIL bring-up so future sessions don’t repeat the same debugging loops. Scope is intentionally append-only documentation: no code, behavior, or parameter semantics are changed.

• New runbook: staged HIL bring-up

  Added docs/hil_bringup_checklist.md with a 6-stage procedure, explicit gate model (build/launch/runtime + HIL engage gate), verification points between gates, and safe disengage order.

• Status addendum: operational lessons from 2026-06-16

  Appended a new section to STATUS.md documenting:

  • the three-gate model (+ HIL fourth gate),
  • service-call hang from launching terminal (and workaround),
  • frozen-at-construction wave/hydro params vs apparent runtime mutability,
  • why hydro_torque_raw = 0.0 can be physically valid,
  • follow-up low-priority consolidation PR ideas.

• Discoverability update

  Added docs/hil_bringup_checklist.md to the README.md “Sub-package documentation” list directly after docs/sea-stack-integration.md.

- [`docs/sea-stack-integration.md`](docs/sea-stack-integration.md) — SEA-Stack hydrodynamics integration: pipeline, parameters, engage gate, telemetry, troubleshooting
- [`docs/hil_bringup_checklist.md`](docs/hil_bringup_checklist.md) — staged HIL bring-up procedure with the two-gate safety model, verification commands per stage, and the "common gotchas" learned during the 2026-06-16 SIL bring-up