Update /setup-github to copy over the custom commands to .github/commands

[jerop]

This is a follow up after #377

[gemini-cli]

🤖 Hi @jerop, I've received your request, and I'm working on it now! You can track my progress in the logs for more details.

[gemini-cli]

🤖 I'm sorry @jerop, but I was unable to process your request. Please see the logs for more details.