docs(start): add Docker with Bun and improved Cloudflare setup for hosting guide

[bapspatil]

Summary

• Improved Cloudflare Workers configuration using wrangler.jsonc
• Added Docker containerization guidance using Bun

What changed

• Deleted Cloudflare Pages references
• Left Cloudflare Workers section intact, including wrangler.jsonc example and Deploy to Cloudflare button notes
• Left Docker with Bun section intact, including multi-stage Dockerfile, .dockerignore, optional docker-compose.yaml, and Coolify notes

Why

• Consolidate Cloudflare guidance around Workers only
• Align with project preferences for Bun and wrangler.jsonc (wrangler.toml is outdated)
• Provide developers with the option to self-host their TanStack Start app on their own server with Docker

How to test

• Docker with Bun
  1. Set target: 'bun' in vite.config.ts
  2. Build image: docker build -t my-tanstack-start-app .
  3. Run: docker run --rm -p 8080:5173 -e HOST=0.0.0.0 -e PORT=5173 my-tanstack-start-app
  4. Visit http://localhost:8080

Notes

• Bun deployment guidance requires React 19 or newer
• Prefer wrangler.jsonc over TOML
• Server listens on PORT default 5173

Breaking changes

• None