Add pdf-world static frontend (Three.js + PDF.js + IndexedDB)

[PGuuu]

Motivation

• Create a new pdf-world static frontend project that converts dropped PDFs into 3D books and previews them in a right-side viewer.
• Integrate a lightweight stack using Three.js for 3D, PDF.js for rendering, and IndexedDB for offline storage.
• Ensure the site runs on a local static server / Live Server and provide steps for GitHub Pages deployment.

Description

• Added pdf-world/index.html which wires up styles, an importmap for three, and loads pdfjs-dist as a module and app.js via type="module".
• Added pdf-world/style.css implementing the HUD layout, viewer, pager, and drop overlay styles used by the UI.
• Added pdf-world/db.js implementing simple IndexedDB helpers: dbPut, dbGetAll, dbDelete, and dbClear for storing PDF ArrayBuffers.
• Added pdf-world/app.js implementing the app logic: drag-&-drop import, IndexedDB persistence, Three.js scene and book meshes, click-to-select, and PDF viewer + paging using window.__pdfjsLib.

Testing

• Launched a local static server with python -m http.server in pdf-world/ and confirmed it served index.html on http://127.0.0.1:8000/ successfully.
• Executed a Playwright script that opened http://127.0.0.1:8000/index.html and captured a full-page screenshot saved to artifacts/pdf-world.png, which completed successfully.
• Committed the new files to the repo (pdf-world/) and created the PR; automated checks described above succeeded.

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Codex Task