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/mailer.js

@@ -1,11 +1,28 @@
-'use strict';
+import assert from 'node:assert';
+import BoxError from './boxerror.js';
+import * as branding from './branding.js';
+import constants from './constants.js';
+import * as dashboard from './dashboard.js';
+import debugModule from 'debug';
+import ejs from 'ejs';
+import * as mailServer from './mailserver.js';
+import nodemailer from 'nodemailer';
+import path from 'node:path';
+import safe from 'safetydance';
+import * as translations from './translations.js';
 
-exports = module.exports = {
+const debug = debugModule('box:mailer');
+
+const _mailQueue = []; // accumulate mails in test mode;
+
+function clearMailQueue() {
+    _mailQueue.length = 0;
+}
+
+export {
     passwordReset,
-
     sendInvite,
     sendNewLoginLocation,
-
     backupFailed,
     certificateRenewalError,
     appDown,
@@ -14,26 +31,12 @@ exports = module.exports = {
     rebootRequired,
     boxUpdateError,
     lowDiskSpace,
-
     sendTestMail,
-
-    _mailQueue: [] // accumulate mails in test mode
+    _mailQueue,
+    clearMailQueue,
 };
 
-const assert = require('node:assert'),
-    BoxError = require('./boxerror.js'),
-    branding = require('./branding.js'),
-    constants = require('./constants.js'),
-    dashboard = require('./dashboard.js'),
-    debug = require('debug')('box:mailer'),
-    ejs = require('ejs'),
-    mailServer = require('./mailserver.js'),
-    nodemailer = require('nodemailer'),
-    path = require('node:path'),
-    safe = require('safetydance'),
-    translations = require('./translations.js');
-
-const MAIL_TEMPLATES_DIR = path.join(__dirname, 'mail_templates');
+const MAIL_TEMPLATES_DIR = path.join(import.meta.dirname, 'mail_templates');
 
 // This will collect the most common details required for notification emails
 async function getMailConfig() {
@@ -53,7 +56,7 @@ async function sendMail(mailOptions) {
     assert.strictEqual(typeof mailOptions, 'object');
 
     if (constants.TEST) {
-        exports._mailQueue.push(mailOptions);
+        _mailQueue.push(mailOptions);
         return;
     }