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/runtimes/child-process-runtime.ts

@@ -3,7 +3,6 @@ import { fork, type ChildProcess } from "node:child_process";
 import { fileURLToPath } from "node:url";
 import { dirname, join } from "node:path";
 import type {
-  Task,
   TaskStore,
   CentralCore,
 } from "@fusion/core";
@@ -19,7 +18,6 @@ import { IpcHost } from "../ipc/ipc-host.js";
 import {
   START_RUNTIME,
   STOP_RUNTIME,
-  GET_STATUS,
   GET_METRICS,
   TASK_CREATED,
   TASK_MOVED,