Update requirements.txt to specify dependencies and remove commented lines

requirements.txt

@@ -1,5 +1,5 @@
 marimo
-# Or a specific version
-# marimo>=0.9.0
-
-# Add other dependencies as needed
+pydantic>=2.12.4
+pydantic-ai>=0.0.13
+openai
+python-dotenv>=1.2.1