Comprehensive deployment documentation

Adds manual/deploy.md covering deployment strategies for various platforms
including traditional servers (Node.js, Bun, Deno) and serverless
environments (Cloudflare Workers, Deno Deploy). Includes platform-specific
configuration, scaling considerations, and observability guidance.

Closes https://github.com/fedify-dev/fedify/issues/16
Closes https://github.com/fedify-dev/fedify/issues/244