feat(FN-1757): clear residual lint debt in engine package

- Remove unused imports across 25 files in engine package
- Remove unused variable declarations in ipc-worker.ts, child-process-runtime.ts, and mission-autopilot.ts
- Clean up unnecessary imports in agent-instructions.ts, agent-tools.ts, cron-runner.ts, executor.ts, and other modules
- Minor cleanup in notifier.ts, peer-exchange-service.ts, pi.ts, plugin-runner.ts, and other files
- Improves code quality and reduces potential confusion from unused code

packages/engine/src/project-manager.ts

@@ -1,5 +1,5 @@
 import { EventEmitter } from "node:events";
-import type { Task, CentralCore, RegisteredProject } from "@fusion/core";
+import type { Task, CentralCore } from "@fusion/core";
 import { InProcessRuntime } from "./runtimes/in-process-runtime.js";
 import { ChildProcessRuntime } from "./runtimes/child-process-runtime.js";
 import { RemoteNodeRuntime } from "./runtimes/remote-node-runtime.js";