Modernizing the toolbox for Cloudflare Pages builds

Introduced a new beta build system for Cloudflare Pages with updated default language/tool versions (Node.js 18.16.0, Python 2.7.18/3.10.5, Ruby 3.2.2, Yarn 3.5.1, pnpm 8.2.0) and improved reproducibility via `npm ci` and `yarn --pure-lockfile`. Migrated the build architecture to a modular, sequential Kubernetes init container model, separating repository cloning, build execution, and asset uploading. Implemented a global log collector for streaming build logs to Durable Objects. Enabled build caching by design, allowing persistence and restoration of files between builds.