Use lacinka NPM package in browser UI for Belarusian → Łacinka

[lautsevich]

Motivation

• Replace ad-hoc transliteration logic with the canonical lacinka library to ensure correct, maintained Łacinka rules.
• Provide a client-side experience so users can transliterate names directly in the browser without a Python runtime or server.
• Make it easy to install the library locally via npm instead of relying on a CDN.

Description

• Replace the Python FastAPI service and custom transliteration modules with a static UI: add index.html and transliteration.js that drive the page UI and clipboard interactions.
• Remove custom mapping rules and update transliteration.js to resolve and call the UMD lacinka export when available (falling back to sensible UMD names).
• Add package.json with a lacinka dependency and update index.html to load the UMD bundle from ./node_modules for local usage.
• Update README.md with npm install instructions and browser-run guidance (index.html).

Testing

• No unit tests were added or executed for this change.
• An automated Playwright attempt to exercise the UI and capture a screenshot was run but timed out and did not complete (failed).
• No automated verification of the installed lacinka bundle was performed in CI in this environment.

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Codex Task