feat(FN-1401): integrate PluginRunner into runtime lifecycle

- Integrate PluginRunner into InProcessRuntime for plugin lifecycle management
- Wire plugin:created, plugin:updated, plugin:deleted events through runtime event bus
- Add plugin tools to StepSessionExecutor so plugins can provide tools during step execution
- Fix PluginRunner to pass PluginContext to task lifecycle hooks (onTaskCreated, onTaskUpdated, etc.)
- Add PluginRunner tests covering init/shutdown, timeout isolation, and sync event behavior
- Add InProcessRuntime tests verifying plugin integration
- Update memory documentation with plugin runner lifecycle wiring

packages/engine/src/index.ts

@@ -30,6 +30,7 @@ export { StuckTaskDetector, type StuckTaskDetectorOptions, type DisposableSessio
 export { HeartbeatMonitor, HeartbeatTriggerScheduler, type WakeContext } from "./agent-heartbeat.js";
 export { TokenCapDetector, type TokenCapCheckResult } from "./token-cap-detector.js";
 export { SelfHealingManager, type SelfHealingOptions } from "./self-healing.js";
+export { PluginRunner, type PluginRunnerOptions } from "./plugin-runner.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";