chore: add root main.py for Railpack auto-detection

Railpack requires main.py or app.py at the project root to detect
the start command. Adds a thin wrapper that sets PYTHONPATH for the
src layout and delegates to pr_af.app:main.

Author: santoshkumarradha

main.py

@@ -0,0 +1,9 @@
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).parent / "src"))
+
+from pr_af.app import main
+
+if __name__ == "__main__":
+    main()