fix: catch startup errors and display them instead of crash-looping

streamlit_app.py

@@ -1,12 +1,16 @@
-import sys, os
+import sys, os, traceback
+import streamlit as st
 from pathlib import Path
 
 root = Path(__file__).resolve().parent
 sys.path.insert(0, str(root))
 os.chdir(str(root))
 
-demo = root / "demo" / "streamlit_app.py"
-with open(demo, encoding="utf-8") as f:
-    code = f.read()
-
-exec(compile(code, str(demo), "exec"), {"__file__": str(demo), "__name__": "__main__"})
+try:
+    demo = root / "demo" / "streamlit_app.py"
+    with open(demo, encoding="utf-8") as f:
+        code = f.read()
+    exec(compile(code, str(demo), "exec"), {"__file__": str(demo), "__name__": "__main__"})
+except Exception as e:
+    st.error(f"App failed to load: {e}")
+    st.code(traceback.format_exc())