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

@@ -991,20 +991,20 @@ export function LeftSidebar() {
           </button>
         </div>
 
-        {/* Settings — admin only, navigates to the settings section */}
-        {isAdmin && (
-          <button
-            onClick={() => navigateToSection('settings', {})}
-            className={cn(
-              'flex w-full items-center gap-2 rounded px-2 py-1 text-[12px] hover:bg-surface-2 hover:text-text',
-              currentSection === 'settings' ? 'text-primary' : 'text-text-muted',
-            )}
-            title="Settings"
-          >
-            <Settings className="h-3.5 w-3.5" />
-            Settings
-          </button>
-        )}
+        {/* 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(
+            'flex w-full items-center gap-2 rounded px-2 py-1 text-[12px] hover:bg-surface-2 hover:text-text',
+            currentSection === 'settings' ? 'text-primary' : 'text-text-muted',
+          )}
+          title="Settings"
+        >
+          <Settings className="h-3.5 w-3.5" />
+          Settings
+        </button>
 
         <Footer />
       </div>