Make Cloudflare streaming work end to end and align docs

[jonmumm]

Summary

• make the Cloudflare streaming example work end to end in the deployed environment
• add Cloudflare TURN-backed ICE configuration for both receiver and sender
• harden the Worker/container boundary with typed request parsing, short-lived TURN credentials, debug auth, and seam tests
• isolate stream sessions per receiver instead of routing everyone through one shared singleton session
• refresh the repo docs, agent context, and package READMEs so they match the current working architecture and target OGS integration model

What Changed

• fixed the deployed WebRTC path by minting Cloudflare TURN credentials in the Worker and passing them through the runtime
• added trace IDs and debug tooling to diagnose deployed failures
• fixed Durable Object/container restart behavior and session routing
• added worker seam tests for TURN normalization, debug endpoint auth, and session-scoped routing
• documented the current repo shape: working Cloudflare runtime today, productized OGS SDK direction next
• aligned package READMEs with the actual exported APIs and current maturity level

Current State

• local Bun/container streaming works
• deployed Cloudflare Worker + Durable Object + Container streaming works
• receiver sessions are isolated with x-stream-session-id
• docs now explicitly capture what has been completed and what still needs to be done for productization

Follow-Ups

• gate /ice-servers so TURN credentials cannot be minted anonymously
• define the public OGS-facing stream-kit SDK surface
• add opengame-api control-plane endpoints for cast and stream session lifecycle

Verification

• pnpm test
• pnpm typecheck
• deployed manual verification against the Cloudflare receiver/worker flow