feat: AutoGen multi-agent email system with Commune (30-cell deep-dive)

[shanjairaj7]

Summary

• Adds notebooks/autogen_email_agent.ipynb — a 30-cell deep-dive on building a multi-agent AutoGen system where agents communicate with real humans via Commune email inboxes
• Covers the full architecture: ResearchAgent + OutreachAgent using separate Commune inboxes, FastAPI webhook handler with HMAC verification, asyncio reply queue, and AutoGen GroupChat coordination
• Unique depth: explicit treatment of connection pool exhaustion (why singleton CommuneClient matters), immediate-200 webhook pattern with failure mode illustrated, idempotency via deque, and prompt injection pre-check

What makes this 10x better than typical notebooks

• Common Mistake cell: shows the singleton vs. per-call client anti-pattern with concrete failure mode (100 open connection pools at 100 calls/min)
• ASCII architecture diagram with 3 layers: Python process, Commune API, external email
• Production Warning cells: why not returning 200 immediately causes duplicate delivery (with timeline)
• Webhook explained deeply: HMAC verification with constant-time comparison to prevent timing attacks, idempotency with deque(maxlen=10_000)
• Why one inbox per agent: concrete failure mode for shared inbox (subject-line routing breaks at ~50 threads)
• Every code cell preceded by a markdown "why" cell

Test plan

• Notebook renders correctly in Jupyter/Colab
• Install cell includes all required dependencies
• All code cells have realistic expected output in comments
• Architecture ASCII diagram is readable in GitHub preview