Add llms.txt and llms-full.txt files to improve discoverability and understanding of kubefwd by AI assistants and LLM-powered tools.

Files added:

• docs/llms.txt - Concise index following the llms.txt standard with project summary and links to key documentation
• docs/llms-full.txt - Comprehensive documentation in a single file for LLMs with larger context windows

These files help AI assistants better understand and explain kubefwd to users, improving the developer experience when using AI-powered coding tools.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• Test improvement (new or updated tests)
• Documentation update
• Stability/performance improvement
• Build/CI improvement

Note: New features are developed by maintainers only. See CONTRIBUTING.md for details.

Related Issues

N/A - Proactive improvement for AI/LLM discoverability

Testing

• Ran go test ./... locally
• Tested manually with a Kubernetes cluster
• Added new tests for changes (if applicable)

N/A - Documentation only, no code changes.

Checklist

• My code follows the project's style guidelines (go fmt, go vet)
• I have read CONTRIBUTING.md
• I have updated documentation if needed
• This PR is focused and does not include unrelated changes

Screenshots/Logs (if applicable)

llms.txt structure:

# kubefwd

> Kubernetes bulk port forwarding for local development...

## Documentation
- [Getting Started](https://kubefwd.com/getting-started/)
- [User Guide](https://kubefwd.com/user-guide/)
- [Configuration](https://kubefwd.com/configuration/)
- [REST API](https://kubefwd.com/api-reference/)
- [MCP Integration](https://kubefwd.com/mcp-integration/)

## Key Features
...

## Optional
- [Troubleshooting](https://kubefwd.com/troubleshooting/)
- [Architecture](https://kubefwd.com/architecture/)
...