Fix isProcessAlive using require() in ESM — broke all Node.js Windows tests

The Windows process check used `require('child_process')` which doesn't
exist in Node.js ESM modules (only works in Bun which supports require
in ESM). This caused every isProcessAlive() call to throw, be caught,
and return false — making all bridge processes appear dead.

Cascading effects: sessions always showed "crashed", PIDs were null
(bridges got unnecessarily restarted), close couldn't send HTTP DELETE
(thought bridge was dead), and proxy stayed alive after close.

Fix: import execFileSync at module top level (ESM-compatible) and use
execFileSync instead of execSync (also avoids shell injection).

https://claude.ai/code/session_01QA2R1dDEWRrdGUAbX9Qz9B

Author: claude

src/lib/utils.ts

@@ -4,6 +4,7 @@
  */
 
 import { createHash } from 'crypto';
+import { execFileSync } from 'child_process';
 import { homedir } from 'os';
 import { join, resolve, isAbsolute } from 'path';
 import { mkdir, access, constants } from 'fs/promises';
@@ -332,9 +333,7 @@ export function isProcessAlive(pid: number): boolean {
  */
 function isProcessAliveWindows(pid: number): boolean {
   try {
-    // eslint-disable-next-line @typescript-eslint/no-require-imports
-    const { execSync } = require('child_process') as typeof import('child_process');
-    const output = execSync(`tasklist /FI "PID eq ${pid}" /NH`, {
+    const output = execFileSync('tasklist', ['/FI', `PID eq ${pid}`, '/NH'], {
       encoding: 'utf-8',
       stdio: ['pipe', 'pipe', 'pipe'],
       timeout: 5000,