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/test/dns-providers-test.js

@@ -1,20 +1,19 @@
 /* jslint node:true */
+
+import * as common from './common.js';
+import * as dns from '../dns.js';
+import * as domains from '../domains.js';
+import expect from 'expect.js';
+import { DNS as GCDNS } from '@google-cloud/dns';
+import nock from 'nock';
+import * as _ from '../underscore.js';
+
 /* global it:false */
 /* global describe:false */
 /* global before:false */
 /* global beforeEach:false */
 /* global after:false */
 
-'use strict';
-
-const common = require('./common.js'),
-    dns = require('../dns.js'),
-    domains = require('../domains.js'),
-    expect = require('expect.js'),
-    GCDNS = require('@google-cloud/dns').DNS,
-    nock = require('nock'),
-    _ = require('../underscore.js');
-
 describe('dns provider', function () {
     const { setup, cleanup, auditSource, domain } = common;
     const domainCopy = Object.assign({}, domain); // make a copy