fix: update backend module path in start.sh to reflect new structure

start.sh

@@ -1,3 +1,3 @@
 #!/bin/sh
 node frontend/server.js &
-python -m uvicorn backend.main:app --host 0.0.0.0 --port 8000
+python -m uvicorn backend.app.main:app --host 0.0.0.0 --port 8000