fix(harness): make doctor distinguish clean, debt, and unreachable authority

Parent: #384 (P1-4b).

## Scope
Replace doctor success wording that claims a complete audit chain when WARNs or an unreachable GitHub authority exist.

## Acceptance
- Outcomes distinguish CLEAN, PASS_WITH_DEBT, and FAIL/UNREACHABLE.
- GitHub unavailable and feature-list load failures cannot be rendered as fully healthy.
- Exit-code policy is explicit and tested.

Delivery discipline: one issue, one worker branch, one PR.

Start at the doctor command and its harness, then trace how WARNs, GitHub authority failures, and feature-list load failures are rendered and how exit codes are selected. Done means CLEAN, PASS_WITH_DEBT, and FAIL/UNREACHABLE are distinct, unhealthy cases are not reported as fully healthy, and the exit-code policy is covered by tests.

Written by the indexing model from the issue text.