Add standalone mode with @simpleworkjs/orm-backed user/host stores

- Add standalone.enabled config flag to switch between LDAP+SSO and
  ORM-backed backends without changing the production code path
- New ORM models: StandaloneUser (uid, passwordHash, sshPublicKeys,
  groups) and StandaloneHost (slug, displayName, kind, metadata)
- user_file.js and hosts_file.js implement the same interfaces as the
  LDAP client and accessibleHosts() respectively
- models/user_ldap.js and utils/access.js become conditional facades
  that delegate based on conf.standalone.enabled at require time
- Zero changes to ssh_server.js core logic, bridge.js, key_inject.js,
  tui_picker.js, or any other consumer
- Fix ssh_server.js: use ?? instead of || for listenPort (0 is falsy)
- Fix ssh_server.js: register session listeners before awaiting
  audit.create() so client exec/shell requests aren't rejected
- Patch StringField.toSequelize() and IntegerField.toSequelize() to
  pass through primaryKey (the ORM's UUIDField already does this)
- 47 tests pass (24 existing + 15 new unit + 3 existing integration
  + 5 new standalone integration)
- Defaults to SQLite; any Sequelize dialect works via conf.orm

Co-Authored-By: Claude <noreply@anthropic.com>

nodejs/models/standalone_user.js

@@ -0,0 +1,36 @@
+'use strict';
+
+// ORM model for standalone-mode users. Stored in the configured SQL database
+// (default SQLite) when conf.standalone.enabled is true. The user_file.js
+// wrapper translates between this model and the LDAP-client interface that
+// ssh_server.js and key_inject.js expect.
+
+const { Model, fields } = require('@simpleworkjs/orm');
+
+// Patch: StringField.toSequelize() and IntegerField.toSequelize() don't pass
+// through primaryKey / autoIncrement (unlike UUIDField which does). Fix them
+// so string and int primary keys work.
+const origStringToSeq = fields.StringField.prototype.toSequelize;
+fields.StringField.prototype.toSequelize = function () {
+  const def = origStringToSeq.call(this);
+  if (this.primaryKey) def.primaryKey = true;
+  return def;
+};
+const origIntToSeq = fields.IntegerField.prototype.toSequelize;
+fields.IntegerField.prototype.toSequelize = function () {
+  const def = origIntToSeq.call(this);
+  if (this.primaryKey) def.primaryKey = true;
+  if (this.autoIncrement) def.autoIncrement = true;
+  return def;
+};
+
+class StandaloneUser extends Model {
+  static fields = {
+    uid: { type: 'string', primaryKey: true },
+    passwordHash: { type: 'string', isPrivate: true },
+    sshPublicKeys: { type: 'json', default: [] },
+    groups: { type: 'json', default: [] },
+  };
+}
+
+module.exports = StandaloneUser;