Remove the inherited create-react-app monorepo (#5)

Removes ~116,000 lines of upstream create-react-app source that nothing in this
repository builds, tests, or ships: packages/, docusaurus/, test/, tasks/, the
changelogs, CONTRIBUTING.md, SECURITY.md and the screencast assets, along with
the configs that only scoped to those directories -- lerna.json, netlify.toml,
the eslint/prettier/alex configs, and the upstream .github meta files.

LICENSE is kept; the fork lineage is real. CODE_OF_CONDUCT.md and the pull
request template are generic and still apply.

README.md described a create-react-app app at the repo root that does not
exist, since the root has no src/ or public/. Rewritten to describe my-app and
public_html, how each is built and deployed, and this history.

Verified with the CI steps from my-app -- npm ci, npm run lint, npm run build --
and by grepping the tree for references to every removed path.

Author: niteeshkanna-sh