Improve Harness Doctor evidence messages

[baskduf]

Goal

Make Harness Doctor output more actionable without changing the scoring philosophy.

Scope

• Review scripts/harness_doctor.py output for vague evidence or missing-item messages.
• Improve message clarity while keeping the baseline scan lightweight.
• Add or update tests in tests/test_harness_doctor.py for changed wording or behavior.

Acceptance Criteria

• Messages help maintainers understand the next durable artifact to add.
• The scan remains diagnostic only and does not modify files.
• python -m unittest tests.test_harness_doctor passes.
• python scripts/harness_doctor.py --target . still reports expected baseline evidence.

References

• ROADMAP.md
• CONTRIBUTING.md
• docs/scoring/harness-score-rubric.md