Add LLM filtering pattern, .env.example, and workflows/lib

- Add .env.example with LLM_API_URL, LLM_MODEL, LLM_API_KEY
- Add .gitignore to exclude .env
- Add Pattern 5 (LLM filtering) to notebook-patterns.md
- Track workflows/lib with llm_call helper using mirascope
- Update README with LLM setup step and updated project structure

workflows/lib/__init__.py

@@ -0,0 +1,5 @@
+"""Library modules for contact analysis workbooks."""
+
+from lib.llm import llm_call
+
+__all__ = ["llm_call"]