Refresh diagnostics documentation

[codeforester]

Summary

• add BASE-P172 to the doctor finding table
• split shipped observability history docs from planned commands and link the tracker
• document Python-backed diagnostic subprocess timeout behavior

Verification

• git diff --check
• PYTHONPATH=lib/python:cli/python "$HOME/.base.d/base/.venv/bin/python" -m pytest cli/python/base_setup/tests/test_diagnostics.py cli/python/base_setup/tests/test_artifact_probe_timeouts.py -q

Closes #1260
Closes #1261
Closes #1273
Closes #1280