feat: add production pattern notebooks (CrewAI 02, OpenAI Agents 02, LangChain 03)

[shanjairaj7]

Summary

• crewai_02_production_patterns.ipynb — thread persistence via SQLite ThreadRegistry, multi-inbox routing, deterministic idempotency keys, exponential backoff retry with dead-letter queue, and a webhook-ready ProductionEmailTool (18 cells)
• openai_agents_02_patterns.ipynb — thread continuity via RunContextWrapper dataclass, extraction schemas with cost/latency comparison table, parallel asyncio agents, prompt injection defense with sanitize_for_llm + recipient domain validation (19 cells)
• langchain_03_production.ipynb — singleton client pattern, search.threads() context building, delivery.metrics() health checks with alerting thresholds, delivery.suppressions() audit, FastAPI async webhook handler with signature verification, and sms.send() escalation for critical urgency emails (18 cells)

All notebooks have simulated output cells on every API-calling code cell (3-way semantic pair: markdown prose + code + output).

Test plan

• Open each notebook in Colab to verify cell rendering
• Confirm all code cells have simulated outputs
• Verify no phantom API calls (search/sms/delivery all namespaced correctly)