fix(sidebar): show Settings entry to non-admin users

Companion to 4c7e981 — the SettingsPage was opened to non-admins but
the LeftSidebar still gated the entry button on isAdmin, so non-admins
had no way to reach it. The page itself is the source of truth for
which tabs and controls are visible per role.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/layout/LeftSidebar.tsx

@@ -991,8 +991,9 @@ export function LeftSidebar() {
           </button>
         </div>
 
-        {/* Settings — admin only, navigates to the settings section */}
-        {isAdmin && (
+        {/* Settings — visible to all signed-in users; the panel itself
+            hides admin-only tabs (Users) and admin-only controls inside
+            the AI tab. Library + Nextcloud config is per-user. */}
         <button
           onClick={() => navigateToSection('settings', {})}
           className={cn(
@@ -1004,7 +1005,6 @@ export function LeftSidebar() {
           <Settings className="h-3.5 w-3.5" />
           Settings
         </button>
-        )}
 
         <Footer />
       </div>