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/package.json

@@ -25,6 +25,7 @@
     "@simpleworkjs/ldap": "^1.0.0",
     "@simpleworkjs/directory-schema": "^1.0.0",
     "@simpleworkjs/oidc-client": "^1.0.0",
+    "@simpleworkjs/orm": "^0.2.8",
     "bcrypt": "^6.0.0",
     "bootstrap": "^5.3.8",
     "compression": "^1.8.1",