fix and unify devui samples (#5025)

python/samples/02-agents/devui/main.py

@@ -0,0 +1,32 @@
+# Copyright (c) Microsoft. All rights reserved.
+
+"""Launch DevUI with folder discovery for the samples in this directory.
+
+This sample demonstrates:
+- Loading a shared root `.env` file for the DevUI samples folder
+- Starting DevUI in directory discovery mode for this folder
+- Using root-level settings as fallbacks for discovered samples
+"""
+
+from pathlib import Path
+
+from agent_framework.devui import serve
+from dotenv import load_dotenv
+
+
+def main() -> None:
+    """Load the root .env file and launch DevUI with folder discovery."""
+    samples_dir = Path(__file__).resolve().parent
+
+    # 1. Load shared defaults for the samples in this folder.
+    load_dotenv(samples_dir / ".env")
+
+    # 2. Start DevUI and discover entities from this directory.
+    serve(entities_dir=str(samples_dir), auto_open=True)
+
+
+if __name__ == "__main__":
+    main()
+
+# Sample output:
+# Starting Agent Framework DevUI on 127.0.0.1:8080