docs: fix the Jupyter tutorial's Compose indentation and release link, and explain the auth modes and per-run kernels

[silentoplayz]

Summary

The Jupyter tutorial's Compose example had every key flush left, so it was not valid YAML. It is re-indented, with the extra_hosts entry that makes host.docker.internal resolve on Linux. The Open WebUI v0.5.15 release link pointed at v0.5.14. The settings table now says these are persisted admin settings seeded once from the environment, that CODE_EXECUTION_JUPYTER_AUTH accepts exactly token or password, and that the CODE_INTERPRETER_* variables default to their CODE_EXECUTION_* twins. The workflow note explains why nothing persists between runs. Each execution starts a fresh kernel and deletes it afterwards.

Related issue or discussion

None.

Checklist

• I have reviewed the relevant documentation and matched the existing style.
• This PR meets Open WebUI's contribution standards: it is accurate, relevant to users, narrowly scoped, maintainable, and not promotional content, advertising, lead generation, SEO placement, or a request to list a product, service, provider, integration, gateway, tool, or company primarily for visibility.
• I understand that PRs that do not meet these standards may be closed without review and will not be merged. Repeated, low-quality, off-topic, promotional, or intentionally misleading submissions may result in the contributor being blocked from future participation in Open WebUI repositories.

Notes for reviewers

Sources on dev: routers/utils.py and utils/code_interpreter.py (auth modes, kernel lifecycle), routers/configs.py (CODE_EXECUTION_CONFIG_KEYS), config.py (the CODE_INTERPRETER_* fallbacks), and CHANGELOG.md for v0.5.15.