Add VFAT implementation plan and update AGENTS.md FAT documentation
916-line plan covering: workspace structure, implementation phases, API
design, build integration, success criteria, test results, and comprehensive
quality assessment (Section 12 with 12 subsections). AGENTS.md updated with
FAT workspace layout, tool verification status, and config integration details.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
vasilito
e3f4ffd1c9