feat: supervise worker with pm2 instead of cron PID-check

Passenger only manages the Next.js app process; the worker now gets
the same crash-recovery/auto-restart via pm2, replacing the cron-driven
PID-file restart hack. Updates README deployment steps accordingly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

worker/cron-check.ts

@@ -1,36 +0,0 @@
-import { existsSync, readFileSync, writeFileSync } from 'fs'
-import { spawn } from 'child_process'
-import path from 'path'
-
-const PID_FILE = path.join(__dirname, 'worker.pid')
-
-function isRunning(pid: number): boolean {
-  try {
-    process.kill(pid, 0)
-    return true
-  } catch {
-    return false
-  }
-}
-
-if (existsSync(PID_FILE)) {
-  const pid = parseInt(readFileSync(PID_FILE, 'utf-8').trim(), 10)
-  if (!isNaN(pid) && isRunning(pid)) {
-    console.log(`[cron-check] worker already running (PID ${pid})`)
-    process.exit(0)
-  }
-}
-
-const child = spawn(
-  process.execPath,
-  [require.resolve('tsx/cli'), path.join(__dirname, 'index.ts')],
-  { detached: true, stdio: 'ignore' }
-)
-child.unref()
-
-if (child.pid) {
-  writeFileSync(PID_FILE, String(child.pid))
-  console.log(`[cron-check] worker started (PID ${child.pid})`)
-}
-
-process.exit(0)