Add Ammo.js wind-flag demo and GitHub Pages deployment workflow

[AlBentley]

Motivation

• Provide a self-contained static demo that demonstrates a soft-body cloth flag driven by Ammo.js and Three.js.
• Enable easy publishing of the demo via GitHub Pages using an automated workflow so static files can be served without installing dependencies.

Description

• Add a static demo entrypoint at index.html that loads Three.js and Ammo.js from CDNs and boots src/main.js which implements the soft-body flag simulation and scene setup.
• Implement the simulation and rendering in src/main.js including physics world setup, cloth soft-body creation, wind animation, and mesh updates, and add styles in src/style.css and a HUD overlay.
• Add README.md with local preview and deployment instructions and include .gitignore to ignore dist/ artifacts.
• Add a GitHub Actions workflow at .github/workflows/deploy.yml to validate src/main.js with node --check, prepare a dist/ artifact, and deploy to GitHub Pages using actions/deploy-pages.

Testing

• No automated tests were executed as part of this PR, but the workflow includes a JavaScript syntax validation step (node --check src/main.js) configured to run on push or manually via workflow dispatch.
• The repository is prepared for GitHub Pages deployment using the added workflow which will perform the node --check and artifact upload steps when run.

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Codex Task