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/sftp.js

@@ -1,28 +1,30 @@
-'use strict';
+import apps from './apps.js';
+import assert from 'node:assert';
+import blobs from './blobs.js';
+import BoxError from './boxerror.js';
+import constants from './constants.js';
+import debugModule from 'debug';
+import * as docker from './docker.js';
+import hat from './hat.js';
+import infra from './infra_version.js';
+import mounts from './mounts.js';
+import path from 'node:path';
+import paths from './paths.js';
+import safe from 'safetydance';
+import services from './services.js';
+import shellModule from './shell.js';
+import * as volumes from './volumes.js';
 
-exports = module.exports = {
+const debug = debugModule('box:sftp');
+const shell = shellModule('sftp');
+
+const DEFAULT_MEMORY_LIMIT = 256 * 1024 * 1024;
+
+export {
     start,
-
-    DEFAULT_MEMORY_LIMIT: 256 * 1024 * 1024
+    DEFAULT_MEMORY_LIMIT,
 };
 
-const apps = require('./apps.js'),
-    assert = require('node:assert'),
-    blobs = require('./blobs.js'),
-    BoxError = require('./boxerror.js'),
-    constants = require('./constants.js'),
-    debug = require('debug')('box:sftp'),
-    docker = require('./docker.js'),
-    hat = require('./hat.js'),
-    infra = require('./infra_version.js'),
-    mounts = require('./mounts.js'),
-    path = require('node:path'),
-    paths = require('./paths.js'),
-    safe = require('safetydance'),
-    services = require('./services.js'),
-    shell = require('./shell.js')('sftp'),
-    volumes = require('./volumes.js');
-
 async function ensureKeys() {
     for (const keyType of [ 'rsa', 'ed25519' ]) {
         const privateKey = await blobs.get(`sftp_${keyType}_private_key`);
@@ -54,7 +56,7 @@ async function start(existingInfra) {
 
     const serviceConfig = await services.getServiceConfig('sftp');
     const image = infra.images.sftp;
-    const memoryLimit = serviceConfig.memoryLimit || exports.DEFAULT_MEMORY_LIMIT;
+    const memoryLimit = serviceConfig.memoryLimit || DEFAULT_MEMORY_LIMIT;
     const cloudronToken = hat(8 * 128);
 
     await ensureKeys();