'No copilot-instructions.md found' notice is misleading when global config exists

### Describe the bug

When opening the Copilot CLI outside of a git repository, the notice `No copilot-instructions.md found. Run /init to generate.` is misleading. it implies no instructions file was found at all, even when a global `~/.copilot/copilot-instructions.md` exists and is being used.

### Affected version

GitHub Copilot CLI 1.0.49.

### Steps to reproduce the behavior

1. Create a global instructions file at `~/.copilot/copilot-instructions.md`
2. Open Copilot CLI from a directory that is not a git repository
3. Observe the notice: `No copilot-instructions.md found. Run /init to generate.`

### Expected behavior

1. Create a global instructions file at `~/.copilot/copilot-instructions.md`
2. Open Copilot CLI from a directory that is not a git repository
3. Observe the notice: `No repository-level copilot-instructions.md found. Run /init to generate.`

### Additional context

_No response_