Build out README and docs

[nficano]

README claims v1.0; CONFORMANCE.md defers to README; no docs/ structure.

Steps:

1. Rewrite README with v1.1 badge, quickstart, package layout, docs pointer
2. Write CONFORMANCE.md with §-by-§ v1.1 coverage
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)