Write and ship a complete Datasette plugin with Claude Code

Our rewrite with extra checks. The poster didn't test it.

Goal: Implement a Datasette plugin that adds /-/os returning pretty-printed JSON about the operating system, with tests and docs.

Inputs (fill in or confirm):
- The plugin repo path
- Target Python and Datasette versions
- Which fields I most care about (distro, kernel, container base image)

Rules:
- Collect as much OS detail as possible using the standard library and safe file reads (/etc/os-release, platform, uname).
- Detect Docker and, where possible, the base image; return null with a reason when unknown.
- Never shell out to commands that need root or network.
- Add tests that pass on Linux and macOS, and document the endpoint in the README.
- Add a README section with an example of the output.

Checkpoint: Ask before publishing a release to PyPI or pushing tags.

If you get stuck: If a detail isn't available on one OS, skip it gracefully instead of failing the request. If a login, CAPTCHA or two-step code appears, stop and ask me to handle it; never guess or store passwords.

Verify before you finish: Run the tests and hit /-/os locally; paste the JSON output.

Output: Code changes, test results, sample output and README section.

Done when: /-/os returns valid JSON on each OS you can test and the tests pass.