Add Event Floor demo app with staff dispatch and gate admission sync

[Ankush523]

Summary

• Adds apps/eventfloor, a live-events demo with two flows in one app:
  • Flow A — Staff dispatch: MLS group room (useNearbyRoom + group: true), seeded roster/PIN sign-in, encrypted staff alerts and acks, optional crowd relay via useMeshRelay (forward-only UI, no payload).
  • Flow B — Gate sync: Lead scanner hosts an admission ledger; gate scanners join and propose scans; duplicate ticket IDs show already used; Sync to platform (mock) ingests by stable scanId with visible duplicates dropped (OutageNet-style HQ strip).
• Introduces shared MeshRelaySession / useMeshRelay in @offline-app-examples/mesh for relay-only multi-hop demos (TTL 3).
• Domain logic and persistence (AsyncStorage for gate/scanner labels and platform sync state) with unit tests for staff sign-in and admission evaluation.
• CI: Android/iOS matrix entries for eventfloor; root README + demo plan updated. iOS scheme trimmed to avoid missing test target.

Test plan

• pnpm install --frozen-lockfile && pnpm typecheck && pnpm lint && pnpm test
• Flow A (3 phones): Sender → Relay (optional) → Receiver; PIN 1001 / 2002; send alert → receiver ack; relay shows neighbors only.
• Flow B (2 phones): Lead + scanner join; admit T-1001 on lead → already used on scanner; Sync to platform twice → dupes dropped increments.
• iOS: cd apps/eventfloor/ios && bundle exec pod install then run on device with Metro.
• Android: pnpm --filter @offline-app-examples/eventfloor android on device/emulator.
• (Follow-up) Record demo-staff.gif and demo-gate.gif for catalogue embed in root README.

Notes

• Demo GIF assets are documented in apps/eventfloor/README.md but not included in this PR.
• Physical devices with Bluetooth enabled are required for mesh behavior; debug builds need Metro.