chore: add app.py entrypoint

app.py

@@ -0,0 +1,7 @@
+import os
+import uvicorn
+
+if __name__ == "__main__":
+    host = "0.0.0.0"
+    port = int(os.environ.get("PORT", "7860"))
+    uvicorn.run("backend.api:app", host=host, port=port)