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/ipc/ipc-host.ts

@@ -1,6 +1,6 @@
 import { EventEmitter } from "node:events";
 import type { ChildProcess } from "node:child_process";
-import type { IpcMessage, IpcCommandType, IpcResponseType } from "./ipc-protocol.js";
+import type { IpcMessage, IpcCommandType } from "./ipc-protocol.js";
 import { OK, ERROR, PONG, generateCorrelationId } from "./ipc-protocol.js";
 import { ipcLog } from "../logger.js";
 
@@ -151,7 +151,7 @@ export class IpcHost extends EventEmitter {
     this.disconnected = true;
 
     // Reject all pending commands
-    for (const [id, pending] of this.pendingCommands) {
+    for (const [_id, pending] of this.pendingCommands) {
       clearTimeout(pending.timeout);
       pending.reject(new Error(`IPC disconnected: ${error.message}`));
     }

packages/engine/src/ipc/ipc-protocol.ts

@@ -10,9 +10,8 @@
  * 3. Worker can also send events unsolicited (task events, health changes)
  */
 
-import type { RuntimeStatus, RuntimeMetrics, ProjectRuntimeConfig } from "../project-runtime.js";
-import type { Task, TaskStore } from "@fusion/core";
-import type { Scheduler } from "../scheduler.js";
+import type { RuntimeStatus, ProjectRuntimeConfig } from "../project-runtime.js";
+import type { Task } from "@fusion/core";
 
 // ── Base Message Types ────────────────────────────────────────────────────
 

packages/engine/src/ipc/ipc-worker.ts

@@ -4,12 +4,6 @@ import {
   OK,
   ERROR,
   PONG,
-  START_RUNTIME,
-  STOP_RUNTIME,
-  GET_STATUS,
-  GET_METRICS,
-  GET_TASK_STORE,
-  GET_SCHEDULER,
   PING,
   ERROR_EVENT,
   isIpcCommand,