docs: Add 9P introduction and Infernode instructions

- Add "What is 9P?" section explaining the protocol for newcomers
- Add comprehensive Infernode (Inferno OS) mounting instructions
- Add troubleshooting section with common issues and solutions
- Add verified test cases section documenting tested scenarios
- Add "How It Works" explanation of the request flow
- Include tips for Infernode users (use 127.0.0.1, create mount point first)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

feat: Initial implementation of llm9p - LLM as 9P filesystem

Exposes Claude as a 9P filesystem, enabling interaction through
standard file operations:

- ask: write prompt, read response (shim pattern)
- model: read/write current model name
- temperature: read/write sampling temperature
- tokens: read-only token count from last response
- new: write to reset conversation
- context: read JSON history, write to add system message
- _example: usage documentation
- stream/chunk: blocking read for streaming responses

Includes:
- Full 9P2000 protocol implementation (stdlib only)
- Anthropic SDK integration with conversation state
- Streaming support

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>