security: log only exception type (never secrets); generic client errors

app.py

@@ -98,7 +98,7 @@ def api_extract():
     try:
         return jsonify(data=extract(text, schema))
     except Exception as e:
-        import sys; print("extract error:", repr(e), file=sys.stderr, flush=True)
+        import sys; print("extract error:", type(e).__name__, file=sys.stderr, flush=True)
         return jsonify(error="Extraction failed — please try again."), 200
 
 PAGE = """<!doctype html><html lang="en"><head><meta charset="utf-8">