Feature/windows

[hanley-development]

Summary

• Add passive Windows support by resolving Codex paths with pathlib instead of hardcoded ~/.codex strings.
• Preserve existing macOS/Linux behavior by defaulting to Path.home() / ".codex" when CODEX_HOME is not set.
• Respect CODEX_HOME when users need to point the tool at a non-default Codex data directory.
• Derive auth.json from the resolved Codex home directory.
• Add stdlib unittest coverage for default and override path behavior.
• Update .gitignore for generated/local files.

README follow-up

README.md was intentionally left unchanged in this PR. A follow-up documentation PR should make these exact updates:

1. In ## Requirements, replace:

- macOS or Linux.
- Local Codex state under `~/.codex` for `local-usage`.
- A Codex login at `~/.codex/auth.json` and network access for `resets`, `online-usage`, `all` and menu quick summaries.

No third-party Python packages are required. Windows is not supported because the script expects Unix-style paths, an executable shebang workflow and a Codex home at `~/.codex`.

with:

- macOS, Linux or Windows.
- Local Codex state under your Codex home directory for `local-usage`.
- A Codex login at `auth.json` inside your Codex home directory and network access for `resets`, `online-usage`, `all` and menu quick summaries.

No third-party Python packages are required. By default, Codex Usage reads Codex data from `Path.home() / ".codex"`. Set `CODEX_HOME` to use a different Codex home directory.

2. In ## Install And Run,
   add

a PowerShell example after the python3 codex_usage.py example:
py -3 .\codex_usage.py
py -3 .\codex_usage.py local-usage

3. In ## Privacy And Authentication, replace:

~/.codex/auth.json

with:

<Codex home>/auth.json

and add:

The Codex home directory is `Path.home() / ".codex"` unless `CODEX_HOME` is set.

4. In ## Troubleshooting, update the authentication troubleshooting workflow at README.md:252.

Current text:

If the script says `~/.codex/auth.json` is missing or malformed, sign in to Codex first, then run the script again. Codex Usage reuses that existing login; it does not ask for, store or need an OpenAI API key.

Replace with:

If the script says `<Codex home>/auth.json` is missing or malformed, sign in to Codex first, then run the script again. Codex Usage reuses that existing login; it does not ask for, store or need an OpenAI API key.

By default, `<Codex home>` is `Path.home() / ".codex"`, so the default auth file remains `~/.codex/auth.json` on macOS/Linux and the equivalent `.codex\auth.json` directory under the user profile on Windows. If your Codex data is stored somewhere else, set `CODEX_HOME` to that directory before running the script.

Test Plan

python -B -m unittest
python -m py_compile .\codex_usage.py
ruff check .\codex_usage.py .\tests
ruff format --check .\codex_usage.py .\tests
pyflakes .\codex_usage.py .\tests

Fixes #2 on merge