feat(FN-1224): add peer gossip protocol for mesh network synchronization

- Add peer exchange types (MeshSyncState, PeerExchangeMessage, PeerGossipConfig) to core types
- Add peer merge and sync methods to CentralCore (mergeProject, syncWithPeer, getMeshState)
- Add mesh sync API endpoints (GET /api/mesh/state, POST /api/mesh/sync)
- Implement PeerExchangeService background gossip engine for periodic peer synchronization
- Add comprehensive tests for CentralCore mesh methods and PeerExchangeService
- Update memory docs with peer gossip protocol documentation

packages/engine/src/index.ts

@@ -32,6 +32,7 @@ export { TokenCapDetector, type TokenCapCheckResult } from "./token-cap-detector
 export { SelfHealingManager, type SelfHealingOptions } from "./self-healing.js";
 export { ProjectManager } from "./project-manager.js";
 export { NodeHealthMonitor } from "./node-health-monitor.js";
+export { PeerExchangeService, type PeerExchangeServiceOptions, type SyncResult } from "./peer-exchange-service.js";
 export { RemoteNodeClient } from "./runtimes/remote-node-client.js";
 export { RemoteNodeRuntime, type RemoteNodeRuntimeConfig } from "./runtimes/remote-node-runtime.js";
 export { StepSessionExecutor } from "./step-session-executor.js";