Remove `.gemini` config (Gemini Code Assist code review discontinued)

[qkitzero]

Background

The Gemini Code Assist for GitHub code review service has been discontinued, so the .gemini configuration in this repository is no longer functional.

Task

• Remove the .gemini/ directory and its files (e.g. config.yaml, styleguide.md)

Notes

This issue was created across all of my repositories that still contain a .gemini configuration.