Update repo documentation

[gmaclennan]

Context

Milestone-doc nice-to-have: "Update documentation in repo."

The architecture and plan docs in docs/ have drifted as the build moved to Expo SDK 56 + rolldown, the map server was re-integrated, Sentry landed phases 3/6/7, and lifecycle/state handling was refactored. README.md, agents.md, and docs/ARCHITECTURE.md need a pass for accuracy before release.

Scope (to refine)

• README integration/setup steps current with the published package + Expo plugin.
• docs/ARCHITECTURE.md reflects current lifecycle/state machine and IPC topology.
• Prune or mark stale plan docs (build-architecture-plan, runtime-alternatives) as historical.
• Cross-check doc references flagged stale in iOS: fold waitForFile into connectWithRetry for parity with Android #53.