step 1

[RaananW]

Summary

This is step 1 for moving static demos from UMD/global BABYLON pages toward compiled ESM demos using @babylonjs/core and related packages.

• Add the compiled demo build pipeline with Vite, TypeScript, ESLint, Prettier, and source-page generation.
• Add a separate Azure DevOps compiled-demo CI that builds after the site build and render-checks demos in Chromium.
• Add shared demo runtime, source-code pages, and render validation with canvas pixel sampling.
• Port the first compiled demo set, including simple scenes, asset-loading demos, render/effect demos, and post-process coverage.
• Track migration status in docs/compiled-demo-migration.md, including unusable or covered legacy demos.

Validation

• npm run demos:ci
• npm run build

Latest local compiled-demo CI checked 19 compiled demos successfully.