packages/relay: add an experimental Node relay runtime

[yanbw]

Summary

• add an experimental Node.js relay runtime for @getpaseo/relay/node
• keep Node relay behavior aligned with the existing Cloudflare relay for both v1 and v2
• add self-hosting docs plus Node-specific unit and E2E coverage

Test Plan

• npm run typecheck --workspace=@getpaseo/relay
• npm run build --workspace=@getpaseo/relay
• cd packages/relay && npx vitest run src/node-adapter.test.ts src/node-adapter.e2e.test.ts src/cloudflare-adapter.test.ts

Notes

• during local verification, src/e2e.test.ts showed intermittent wrangler dev startup timeouts before later passing again on rerun without code changes
• the Cloudflare runtime behavior itself is unchanged in this patch

[cnaron]

Real-world data point in support of this direction. I'm self-hosting via the community project zenghongtu/paseo-relay on the same Seoul VPS that runs my Paseo daemon. From a mainland-China phone:

Metric	relay.paseo.sh (CF)	Self-hosted	Δ
Ping avg (20 pkts)	195ms	107ms	-88ms (-45%)
Packet loss	3–5%	0%	—
TLS handshake avg	540ms	363ms	-177ms
WS single-frame RTT	225ms	155ms	-70ms

Root cause for the CN delta: my ISP routes relay.paseo.sh (CF anycast) to AMS — so the default path crosses Europe. The VPS has a CN-direct route, and collapsing relay + daemon onto the same box removes the bad hop entirely.

For users running Paseo on their own VPS — likely a big slice of the "remote CC" audience — first-party self-host support is a clear win. Happy to test @getpaseo/relay/node builds when they land.