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/backupcleaner.js

@@ -1,25 +1,25 @@
-'use strict';
+import BoxError from './boxerror.js';
+import apps from './apps.js';
+import * as archives from './archives.js';
+import assert from 'node:assert';
+import backups from './backups.js';
+import * as backupFormats from './backupformats.js';
+import * as backupSites from './backupsites.js';
+import constants from './constants.js';
+import debugModule from 'debug';
+import moment from 'moment';
+import path from 'node:path';
+import safe from 'safetydance';
 
-const BoxError = require('./boxerror.js');
+const debug = debugModule('box:backupcleaner');
 
-exports = module.exports = {
+const _applyBackupRetention = applyBackupRetention;
+
+export {
     run,
-
-    _applyBackupRetention: applyBackupRetention
+    _applyBackupRetention,
 };
 
-const apps = require('./apps.js'),
-    archives = require('./archives.js'),
-    assert = require('node:assert'),
-    backups = require('./backups.js'),
-    backupFormats = require('./backupformats.js'),
-    backupSites = require('./backupsites.js'),
-    constants = require('./constants.js'),
-    debug = require('debug')('box:backupcleaner'),
-    moment = require('moment'),
-    path = require('node:path'),
-    safe = require('safetydance');
-
 function applyBackupRetention(allBackups, retention, referencedBackupIds) {
     assert(Array.isArray(allBackups));
     assert.strictEqual(typeof retention, 'object');