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/constants.js

@@ -1,12 +1,10 @@
-'use strict';
-
-const fs = require('node:fs'),
-    path = require('node:path');
+import fs from 'node:fs';
+import path from 'node:path';
 
 const CLOUDRON = process.env.BOX_ENV === 'cloudron',
     TEST = process.env.BOX_ENV === 'test';
 
-exports = module.exports = {
+export default {
     SMTP_SUBDOMAIN: 'smtp',
     IMAP_SUBDOMAIN: 'imap',
 
@@ -90,6 +88,6 @@ exports = module.exports = {
 
     FOOTER: '© %YEAR% [Cloudron](https://cloudron.io)',
 
-    VERSION: process.env.BOX_ENV === 'cloudron' ? fs.readFileSync(path.join(__dirname, '../VERSION'), 'utf8').trim() : '8.0.0-test'
+    VERSION: process.env.BOX_ENV === 'cloudron' ? fs.readFileSync(path.join(import.meta.dirname, '../VERSION'), 'utf8').trim() : '8.0.0-test'
 };