Add personal Unix group member management

Every account gets a personal posixGroup at creation (its primary GID
holder) but there was no way to manage its memberUid list -- add
add/remove endpoints and a profile-page UI (admin-only), reusing the
userSelect widget already built for the manager field.

Bumps to v1.1.9.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KDEx8ghuZR61pqPXc6da9C

nodejs/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "t42-sso-manager",
-  "version": "1.1.8",
+  "version": "1.1.9",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "t42-sso-manager",
-      "version": "1.1.8",
+      "version": "1.1.9",
       "license": "MIT",
       "dependencies": {
         "@fortawesome/fontawesome-free": "^7.3.0",