doc: Remove duplicate Gemini command definitions

Remove the Gemini command wrappers that duplicate the shared agent skills.

Gemini CLI already loads the Codex and Claude skill definitions directly, so keeping these command entries causes duplicate skill loading and command errors.

Delete the redundant .gemini/commands TOML files and rely on the shared skill sources.

Signed-off-by: Jaehyun Kim <jhkim@precisioninno.com>

Author: jhkim-pii