feat(opencode): add TOON RPC and sidecar

[filipeforattini]

Summary

• add authenticated JSON-RPC and TOON-RPC session read endpoints
• add opt-in TOON framing for ACP stdio
• ship a bounded native RPC sidecar in every platform package
• pin and validate release toolchains and artifact identities

Verification

• typechecks pass for protocol, server, opencode, and rpc-sidecar
• 17 RPC/ACP integration tests pass
• 8 native sidecar tests pass
• six Linux/Windows cross-target builds validated
• npm build, pack, clean install, executable mode, and launcher smoke pass
• generated client and release contract checks pass

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}