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/shell-test.js

@@ -1,15 +1,16 @@
 /* jslint node:true */
+
+import BoxError from '../boxerror.js';
+import expect from 'expect.js';
+import path from 'node:path';
+import safe from 'safetydance';
+import shellModule from '../shell.js';
+
+const shell = shellModule('test');
+
 /* global it:false */
 /* global describe:false */
 
-'use strict';
-
-const BoxError = require('../boxerror.js'),
-    expect = require('expect.js'),
-    path = require('node:path'),
-    safe = require('safetydance'),
-    shell = require('../shell.js')('test');
-
 describe('shell', function () {
     describe('spawn', function () {
         it('can run valid program', async function () {
@@ -52,7 +53,7 @@ describe('shell', function () {
         });
 
         it('can sudo valid program', async function () {
-            const RELOAD_NGINX_CMD = path.join(__dirname, '../src/scripts/restartservice.sh');
+            const RELOAD_NGINX_CMD = path.join(import.meta.dirname, '../src/scripts/restartservice.sh');
             const [error] = await safe(shell.sudo([ RELOAD_NGINX_CMD, 'nginx' ], {}));
             expect(error).to.be.ok();
         });