fix(admin): absolute sidebar nav links so /admin URLs don't accumulate (v0.52.2)

The /admin left-rail NavLinks used relative targets (to="users", etc.). Under
the /admin/* nested route a relative link resolves against the current URL, so
each click appended a segment — Users→Allowlist→Graduation yielded
/admin/users/allowlist/graduation instead of /admin/graduation. Use absolute
targets (/admin/<tab>) + `end` for exact active matching.

Patch 0.52.1 → 0.52.2; CHANGELOG updated. Caught by the operator on PPE.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "rfc-app-frontend",
   "private": true,
-  "version": "0.52.1",
+  "version": "0.52.2",
   "type": "module",
   "scripts": {
     "dev": "vite",

frontend/src/components/Admin.jsx

@@ -59,7 +59,8 @@ export default function Admin({ viewer }) {
           {tabs.map(t => (
             <li key={t.path}>
               <NavLink
-                to={t.path}
+                to={`/admin/${t.path}`}
+                end
                 className={({ isActive }) => `admin-rail-link ${isActive ? 'active' : ''}`}
               >
                 {t.label}