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

.env.example

@@ -0,0 +1,3 @@
+LLM_API_URL=https://litellm-notrack.app.monadical.io
+LLM_MODEL=GLM-4.5-Air-FP8-dev
+LLM_API_KEY=xxxxx