Add doctor diagnostics command

[ChengShiLiu16]

Summary

Adds codex-shim doctor, a read-only local diagnostics command for troubleshooting codex-shim setups.

The report is grouped into stable sections and uses OK/WARN/FAIL/INFO statuses with a final summary. It checks Python, dependencies, Codex CLI availability, settings, runtime files, daemon health, ChatGPT/Cursor passthrough availability, proxy loopback bypass, and Codex config wiring.

Safety

doctor is intentionally conservative:

• does not modify config files
• does not start or stop the daemon
• does not call upstream model providers
• does not print API keys, ChatGPT tokens, auth.json contents, prompts, or request bodies

Exit codes

• returns 1 if any FAIL is present
• returns 0 for OK/WARN/INFO-only reports

Tests

• python3 -m compileall codex_shim/ -q
• uv run --isolated --python 3.11 --with aiohttp --with pytest --with pytest-asyncio python -m pytest tests/test_cli_doctor.py -q
• uv run --isolated --python 3.11 --with aiohttp --with pytest --with pytest-asyncio python -m pytest tests/ -q

[OnlyTerp]

Integrated in #36 (codex-shim doctor diagnostics command). Thanks for the contribution — credited in the PR summary.

[OnlyTerp]

Closing as superseded — this work was integrated and merged in #36. Thank you for the contribution!