feat: RBAC multi-user role-based access control

- Add rbac.py with User model, LDAP group-to-role mapping, page/write dependencies
- Proxy auth reads Remote-Groups header to resolve role from LDAP groups
- JWT tokens carry role claim, /me returns role + allowed pages
- Per-router page access control and viewer write protection
- Terminal WebSocket RBAC check
- Frontend filters sidebar links and routes by allowed pages
- Admin-only Settings page and RBAC override endpoints
- Mount rbac.json in docker-compose for page config persistence

dashboard/frontend/src/lib/api.js

@@ -1,6 +1,13 @@
 const BASE = "/api";
 let token = localStorage.getItem("token") || "";
 
+// Current user info populated after auth
+export let currentUser = { username: "", role: "", pages: [] };
+
+export function setCurrentUser(u) {
+  currentUser = u;
+}
+
 export function setToken(t) {
   token = t;
   if (t) localStorage.setItem("token", t);