Enable git-ai when GIT_TRACE is on

[AtnesNess]

Summary

This PR enables git-ai debug logging when the GIT_TRACE environment variable is set. This allows developers debugging Git operations to automatically see git-ai debug output without needing to set additional environment variables.

Changes

• Added GIT_TRACE environment variable check to is_debug_enabled() function
• Added GIT_TRACE environment variable check to is_debug_performance_enabled() function
• Updated documentation comment to reflect that GIT_TRACE now enables debug logging