Add interactive Elementary Operator Atlas app

[DenisValeev]

Motivation

• Convert the provided poster into a properly typeset, accessible, interactive page that matches the toolbox design language.
• Provide an in-app explorer to inspect the primitive operator and derived constructs with keyboard shortcuts and clipboard support.
• Ensure the new app is available offline by updating the offline asset manifest so the toolbox can cache it.

Description

• Add a new static app at apps/elementary-operator/index.html implementing the poster layout, CSS theme tokens, semantic structure, and an accessible UI with domain toggles and operation chips.
• Implement interactive behavior (guarded IIFE) for domain switching (ℝ/ℂ), operation browsing, left/right keyboard shortcuts, live region updates, and a Copy formula action wired to the Clipboard API.
• Wire the new app into the landing page by inserting an Elementary Operator Atlas card in index.html under Labs & tools.
• Regenerate offline-manifest.json so the new HTML asset is included in the offline cache.

Testing

• Ran npm run build:offline which completed successfully and produced an updated offline-manifest.json including the new asset.
• An initial npx playwright test tests/home-navigation.spec.js run failed because Playwright browsers were not installed in the environment.
• Installed browsers with npx playwright install --with-deps chromium and re-ran npx playwright test tests/home-navigation.spec.js, which passed all tests (10 passed).

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Codex Task