feat: _auth.project.settings not found 추가

apps/client/src/routes/_auth.$project.settings.tsx

@@ -1,8 +1,32 @@
 import { createFileRoute, Link, Outlet, useParams } from '@tanstack/react-router';
-import { Calendar, Home, Tag } from 'lucide-react';
+import { Calendar, Home, Tag, AlertTriangle } from 'lucide-react';
+import { Card, CardContent } from '@/components/ui/card';
+import { Button } from '@/components/ui/button';
 
 export const Route = createFileRoute('/_auth/$project/settings')({
   component: ProjectSettingsLayout,
+  notFoundComponent: () => (
+    <div className="flex h-full items-center justify-center p-4">
+      <Card className="w-full max-w-md border bg-white">
+        <CardContent className="space-y-6 p-6 text-center">
+          <AlertTriangle className="mx-auto h-12 w-12 text-yellow-500" />
+          <div className="space-y-2">
+            <h2 className="text-2xl font-semibold text-gray-900">Page not found</h2>
+            <p className="text-sm text-gray-500">Sorry, the page could not be found.</p>
+          </div>
+          <div className="flex justify-center space-x-3">
+            <Button
+              variant="outline"
+              onClick={() => window.history.back()}
+              className="hover:bg-[#f2f2f2] hover:text-black"
+            >
+              Go Back
+            </Button>
+          </div>
+        </CardContent>
+      </Card>
+    </div>
+  ),
 });
 
 const SETTINGS_LINKS = [