Build out README and CONFORMANCE

[nficano]

CONFORMANCE.md is one line; README has no docs/ pointer. Build out documentation matching TS depth:

1. Rewrite README with v1.1 badge/lede, install snippet, quickstart, crate layout, link to docs
2. Write proper CONFORMANCE.md with section-by-section coverage of v1.1 spec
3. Add docs/guides/{auth,delegation,errors,job-events,jobs,leases,observability,resume,sessions,vendor-extensions}.md
4. Add docs/architecture.md, docs/getting-started.md, docs/transports.md, docs/troubleshooting.md

---

Audit reference: ARCP SDK Audit v1.1 (2026-05-19)