Langfuse LLM tracing example notebook

[kiyeonjeon21]

Priority: P2

Langfuse is running but has no sample tracing. Create a notebook demonstrating LLM observability.

What to do

• Create notebooks/06-langfuse-tracing.ipynb
• Use Langfuse Python SDK to create traces, spans, and generations
• Log prompts, completions, latency, token usage (mock data OK)

Acceptance criteria

• Notebook runs with ai-ml-platform recipe
• At least 3 traces visible in Langfuse UI at :3002
• Works without external LLM API key (uses mock data)
• Documents how to connect real API keys