fix: preserve truth in doctor and lane status

[jeffhuber]

Summary

• make merge-authority review hygiene warn instead of pass when workflow file presence was not verified
• make lanes status render GitHub-unavailable PR/workflow/gate sections as unavailable, not empty
• document the safer interpretation for first-run hygiene warnings and lane-status next actions

Verification

• scripts/dev-python -m unittest tests.test_doctor_provider_review_hygiene tests.test_doctor_registry tests.test_lane_status
• scripts/dev-python -m ruff check src/code_mower/doctor_checks/provider_review_hygiene.py src/code_mower/lane_status.py tests/test_doctor_provider_review_hygiene.py tests/test_lane_status.py
• scripts/dev-python -m code_mower.cli lanes status --repo codemower-ai/code-mower --json
• scripts/dev-python -m code_mower.cli doctor --adoption --repo codemower-ai/code-mower --json
• scripts/dev-python scripts/privacy_scan.py
• scripts/dev-python -m pytest

Closes #540.

[gitar-bot]

Code Review ✅ Approved

Fixes doctor and lane status to preserve truth by warning when workflow file presence is unverified and rendering unavailable GitHub sections accurately instead of empty. No issues found.

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[jeffhuber]

Claude audit (merge-authority lane)

Head SHA: 2205a1d03b6a868826f16f4138ad92c9de7483c2
Findings: P0=0, P1=0, P2=0, P3=1 (blocker policy: any P0/P1/P2 -> BLOCKED)

Claude Audit: PASS

Summary:

Truth-preserving fixes to doctor review_hygiene check and lane_status next_action/render_text; well tested, no P0-P2 issues found.

Findings:

• [P3] No blocking issues -- src/code_mower/lane_status.py:328
  Finding ID: claude:13ae01a11129777a53e7
  No blocker findings; change is a correctness fix consistent with tests and docs.