Add Cloudflare Worker deployment setup

[ianmuchyri]

Summary

• add a Cloudflare Worker entrypoint for serving docs images, diagrams, and screenshots from the shared R2 bucket
• configure Wrangler static assets with run_worker_first routes and the IMAGES_BUCKET binding
• add Cloudflare _headers/_redirects plus maintainer image publishing docs and script
• wire MDX image URLs through the new /docs/synth R2-backed paths

Validation

• pnpm types:check
• pnpm run build
• pnpm exec wrangler deploy --dry-run
• pnpm exec biome check package.json source.config.ts wrangler.jsonc lib/remark-doc-images.ts workers/image-proxy.ts workers/r2-proxy.ts scripts/publish-image.mjs

Note: full pnpm run lint still reports pre-existing unrelated issues in app/[[...slug]]/page.tsx, mdx-components.tsx, lib/base-path.ts, and lib/metadata.ts, plus a Biome schema version warning.