docs(examples): add agentic loop demo with real LLM integration

Comprehensive example showcasing AgentLoop's autonomous problem-solving:
- Demo 1: Multi-step coding (create → read → edit → verify)
- Demo 2: Streaming events (real-time tool/text visibility)
- Demo 3: Planning mode (task decomposition + goal tracking)
- Demo 4: Multi-turn conversation (context preservation)
- Demo 5: Skills-augmented code review (built-in skills)
- Demo 6: Resilient session (parse retries, timeout, circuit breaker)

All demos use isolated temp workspaces and real LLM configuration.

Author: ZhiXiao-Lin