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/utils/hosts_file.js

@@ -0,0 +1,30 @@
+'use strict';
+
+// ORM-backed host inventory for standalone mode. Implements the same interface
+// as utils/access.js so ssh_server.js works unchanged: accessibleHosts(user)
+// returns an array of host resources the user may reach.
+//
+// In standalone mode all hosts in the inventory are accessible to every
+// authenticated user — there is no group-based filtering. The _user parameter
+// is accepted for interface compatibility but ignored.
+
+const StandaloneHost = require('../models/standalone_host');
+
+async function accessibleHosts(_user) {
+  const hosts = await StandaloneHost.list({ where: { kind: 'host' } });
+  // The ORM returns model instances; map to plain objects matching the shape
+  // that target_match.js and tui_picker.js expect.
+  return hosts.map((h) => ({
+    id: h.slug, // slug doubles as the stable id in standalone mode
+    kind: h.kind,
+    slug: h.slug,
+    displayName: h.displayName,
+    metadata: h.metadata || {},
+  }));
+}
+
+function clearCache() {
+  // No cache in standalone mode — every call reads from the DB.
+}
+
+module.exports = { accessibleHosts, clearCache };