Fix matrix path in app.py

app.py

@@ -4,7 +4,7 @@ from pathlib import Path
 
 # Add backend to sys.path so we can import modules correctly
 # We add both backend/ and backend/code to the path
-backend_path = Path(__file__).parent / "backend"
+backend_path = Path(__file__).parent / "matrix"
 sys.path.append(str(backend_path))
 sys.path.append(str(backend_path / "code"))