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>

syslog.js

@@ -1,19 +1,19 @@
 #!/usr/bin/env node
 
-'use strict';
+import debugModule from 'debug';
+import fs from 'node:fs';
+import net from 'node:net';
+import path from 'node:path';
+import paths from './src/paths.js';
+import util from 'node:util';
 
-exports = module.exports = {
+const debug = debugModule('syslog:server');
+
+export {
     start,
     stop
 };
 
-const debug = require('debug')('syslog:server'),
-    fs = require('node:fs'),
-    net = require('node:net'),
-    path = require('node:path'),
-    paths = require('./src/paths.js'),
-    util = require('node:util');
-
 let gServer = null;
 
 // https://docs.docker.com/engine/logging/drivers/syslog/
@@ -97,6 +97,6 @@ async function main() {
     });
 }
 
-if (require.main === module) {
+if (process.argv[1] === import.meta.filename) {
     main();
 }