Migrate codebase from CommonJS to ES Modules

- Convert all require()/module.exports to import/export across 260+ files
- Add "type": "module" to package.json to enable ESM by default
- Add migrations/package.json with "type": "commonjs" to keep db-migrate compatible
- Convert eslint.config.js to ESM with sourceType: "module"
- Replace __dirname/__filename with import.meta.dirname/import.meta.filename
- Replace require.main === module with process.argv[1] === import.meta.filename
- Remove 'use strict' directives (implicit in ESM)
- Convert dynamic require() in switch statements to static import lookup maps
  (dns.js, domains.js, backupformats.js, backupsites.js, network.js)
- Extract self-referencing exports.CONSTANT patterns into standalone const
  declarations (apps.js, services.js, locks.js, users.js, mail.js, etc.)
- Lazify SERVICES object in services.js to avoid circular dependency TDZ issues
- Add clearMailQueue() to mailer.js for ESM-safe queue clearing in tests
- Add _setMockApp() to ldapserver.js for ESM-safe test mocking
- Add _setMockResolve() wrapper to dig.js for ESM-safe DNS mocking in tests
- Convert backupupload.js to use dynamic imports so --check exits before
  loading the module graph (which requires BOX_ENV)
- Update check-install to use ESM import for infra_version.js
- Convert scripts/ (hotfix, release, remote_hotfix.js, find-unused-translations)
- All 1315 tests passing

Migration stats (AI-assisted using Cursor with Claude):
- Wall clock time: ~3-4 hours
- Assistant completions: ~80-100
- Estimated token usage: ~1-2M tokens

Co-authored-by: Cursor <cursoragent@cursor.com>

src/apptaskmanager.js

@@ -1,21 +1,21 @@
-'use strict';
+import assert from 'node:assert';
+import BoxError from './boxerror.js';
+import debugModule from 'debug';
+import fs from 'node:fs';
+import locks from './locks.js';
+import path from 'node:path';
+import paths from './paths.js';
+import safe from 'safetydance';
+import * as scheduler from './scheduler.js';
+import tasks from './tasks.js';
 
-exports = module.exports = {
+const debug = debugModule('box:apptaskmanager');
+
+export {
     start,
     scheduleTask
 };
 
-const assert = require('node:assert'),
-    BoxError = require('./boxerror.js'),
-    debug = require('debug')('box:apptaskmanager'),
-    fs = require('node:fs'),
-    locks = require('./locks.js'),
-    path = require('node:path'),
-    paths = require('./paths.js'),
-    safe = require('safetydance'),
-    scheduler = require('./scheduler.js'),
-    tasks = require('./tasks.js');
-
 const gActiveTasks = {}; // indexed by app id
 const gPendingTasks = [];
 let gStarted = false;