piplite 404 warnings on pip install cells (missing local PyPI warehouse)

[mmcky]

Problem

When users activate in-page execution and run %pip install cells (e.g. %pip install openpyxl), piplite outputs red 404 error warnings before falling back to micropip:

Could not fetch https://quantecon.github.io/lecture-wasm/pypi/all.json: 404 Client Error
Could not parse https://quantecon.github.io/lecture-wasm/pypi/all.json: cannot access local variable

The installs still succeed via micropip fallback, but the red errors are confusing for users.

Cause

JupyterLite's piplite tries to fetch a local PyPI warehouse at <base-url>/pypi/all.json before falling back to the Pyodide CDN. No local warehouse is built as part of the myst build process, so the request returns a 404.

Upstream dependency

The mystmd schema for jupyter.lite does not currently expose a pipliteUrls configuration option to suppress or redirect this lookup. The mystmd docs note this as a TODO: "Add the specific list options for custom wheel paths, etc."

A fix requires either:

1. mystmd exposing piplite configuration (e.g. project.jupyter.lite.pipliteUrls: [])
2. Or mystmd building a local PyPI warehouse as part of myst build --html when jupyter.lite: true

Workaround

Suppress output from %pip install cells using :tags: [remove-output] to hide the warnings from users.