Remove legacy non-cf-proxy runtime code

[seveibar]

Summary

• remove the legacy Bun/Winterspec/Fly runtime, route handlers, middleware, UI helpers, and route test suite
• delete obsolete deployment/config artifacts such as Dockerfile, fly.toml, .dockerignore, and generated OpenAPI output
• update root scripts, README, and CI workflows to treat cf-proxy as the only runtime while keeping the SQLite/D1 build pipeline
• clean up remaining worker references to legacy Fly behavior and refresh affected worker tests/formatting

Testing

• bun run typecheck
• bun run typecheck:cf-proxy
• bun run format:check
• bun run test