Add YardGate demo app for MeshServices discover and invoke

[Ankush523]

Summary

• Adds YardGate (apps/yardgate): driver discovers yardgate-gate via MeshServices, submits seeded load/trailer IDs; gate officer approves or denies; optional yard relay phone for multi-hop demos (mesh relay TTL 3).
• Gate UI shows pending check-ins, recent decisions, and a presenter strip (pending / decided / idempotent replays / BLE neighbors).
• Pure TS tests for check-in payload parsing, gate reducer, and idempotent replay on duplicate checkInId.
• Exports shared mesh helpers from @offline-app-examples/mesh (requestNearbyPermissions, host discovery helpers) for service-style apps.
• CI: Android + iOS build matrix entries for yardgate; root README app table updated.

Test plan

• pnpm install && pnpm typecheck && pnpm test
• pnpm --filter @offline-app-examples/yardgate test
• 3 phones: Gate officer → Start as gate; Relay → Start as relay (between driver and gate); Driver → discover gate, submit check-in, receive approve/deny
• With relay in the middle, driver gate list shows hop count > 0 and check-in still completes
• Gate presenter strip: idempotent replays increments when the same checkInId is delivered again after a decision
• iOS device: cd apps/yardgate && npx react-native run-ios --interactive (signing in Xcode if needed)
• Android: pnpm --filter @offline-app-examples/yardgate android

Notes

• Bluetooth mesh only (SDK 0.27); no Proof of Location; invoke bodies are signed plaintext — demo uses non-secret load IDs only.
• Aligns with nearby service and docs/DEMO_APPS_PLAN.md YardGate scope.