Use agentrc defaults for chief and pr-babysit, document config-free bench locks (#3936)

- Drop TinyUSB's pr-babysit reviewer overrides in favour of agentrc's defaults
- Document the human's yes that authorizes a headless chief to drive a PR
- Allow HIL remote selection and lock forcing only when the task scope names them
- Document that a named-board lock needs no config, while hil_test.py and
  hil_pool_check.py still need the host's config