fix: add openenv back; catch BaseException to surface crash cause

requirements.txt

@@ -14,3 +14,4 @@ scipy>=1.12.0
 matplotlib>=3.8.0
 click>=8.0.0
 python-dotenv>=1.0.0
+openenv>=0.1.0

streamlit_app.py

@@ -1,21 +1,18 @@
-import sys, os, traceback
 import streamlit as st
+import sys, os, traceback
 from pathlib import Path
-import importlib.util
 
 root = Path(__file__).resolve().parent
 sys.path.insert(0, str(root))
 os.chdir(str(root))
 
-demo_file = root / "demo" / "streamlit_app.py"
-
 try:
-    spec = importlib.util.spec_from_file_location("spindleflow_demo", str(demo_file))
-    mod  = importlib.util.module_from_spec(spec)
-    mod.__file__ = str(demo_file)
-    sys.modules["spindleflow_demo"] = mod
-    spec.loader.exec_module(mod)
-    mod.main()
-except Exception as e:
-    st.error(f"SpindleFlow failed to load: {e}")
+    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 SystemExit:
+    pass
+except BaseException as e:
+    st.error(f"SpindleFlow failed: {e}")
     st.code(traceback.format_exc())