Remove temporary demo and test artifacts

[Leonhardmaster2]

Summary

• Remove the temporary Fix Atlas demo site, generated screenshots, Playwright end-to-end suite, framework fixtures, unit-test files, snapshots, and test-only configuration.
• Remove publish-branch automation and obsolete test dependencies so CI only validates the published library package.
• Update the README, issue/discussion audit, changelog, and roadmap to describe the retained package and the temporary nature of the removed validation harness.
• Remove the test-only TestContext hook from the library entry point and refresh the lockfile.

Validation

• pnpm format:check
• pnpm lint
• pnpm typecheck
• pnpm typecheck:ts6
• pnpm build

The remaining documentation image is a library guide asset, not a generated test artifact.