docs: add deprecation notice to main.py

- Mark main.py as deprecated but keep for backward compatibility
- Add warning message when main.py is imported
- Direct users to the new modular structure in src/ directory

Author: jonathan-irvin

main.py

@@ -1,3 +1,13 @@
+# DEPRECATED: This file is kept for backward compatibility with tests
+# New development should use the modular structure in src/ with app.py as the entry point
+
+import warnings
+warnings.warn(
+    "main.py is deprecated. Use the modular structure in src/ with app.py as the entry point",
+    DeprecationWarning,
+    stacklevel=2
+)
+
 import asyncio
 import datetime
 import logging