Move plugin settings access from sidebar to app card

Remove the "Extensions" section from the sidebar nav. Instead, each app
card on the Apps page shows an "Extension" button when the current user
has access to that app's plugin (matched by service ID). The button links
to /settings/plugins/:id alongside the existing admin Settings button.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/Sidebar.tsx

@@ -16,12 +16,11 @@ import {
   Users,
   UsersRound,
   Palette,
-  Puzzle,
 } from "lucide-react";
 import { Button } from "@/components/ui/button";
 import ThemeToggle from "@/components/ThemeToggle";
 import { useAuth } from "@/hooks/useAuth";
-import { getMe, getPlugins, listCategories } from "@/api/client";
+import { getMe, listCategories } from "@/api/client";
 import { cn } from "@/lib/utils";
 
 export default function Sidebar() {
@@ -57,14 +56,6 @@ export default function Sidebar() {
     enabled: appsOpen && docsOpen && !!user,
   });
 
-  const { data: plugins = [] } = useQuery({
-    queryKey: ["plugins"],
-    queryFn: getPlugins,
-    enabled: !!user,
-    // Empty array on 404/error — regular users simply see no plugins
-    retry: false,
-  });
-
   const navItemClass = (isActive: boolean) =>
     cn(
       "flex items-center rounded-lg transition-colors",
@@ -218,40 +209,6 @@ export default function Sidebar() {
           )}
         </NavLink>
 
-        {/* Extensions — visible only when the user has accessible plugins */}
-        {plugins.length > 0 && (
-          <div>
-            {sidebarExpanded ? (
-              <>
-                <div className="px-3 py-1.5">
-                  <span className="text-xs font-semibold uppercase tracking-wider text-muted">
-                    Extensions
-                  </span>
-                </div>
-                <div className="space-y-0.5">
-                  {plugins.map((plugin) => (
-                    <NavLink
-                      key={plugin.id}
-                      to={`/settings/plugins/${plugin.id}`}
-                      className={({ isActive }) => subItemClass(isActive)}
-                    >
-                      <Puzzle className="h-4 w-4 shrink-0" />
-                      <span className="whitespace-nowrap truncate">{plugin.name}</span>
-                    </NavLink>
-                  ))}
-                </div>
-              </>
-            ) : (
-              <NavLink
-                to={`/settings/plugins/${plugins[0].id}`}
-                className={({ isActive }) => navItemClass(isActive)}
-              >
-                <Puzzle className="h-5 w-5 shrink-0" />
-              </NavLink>
-            )}
-          </div>
-        )}
-
         {/* Admin — expandable */}
         {user?.is_admin && (
           <div>