bug:

### Checks

- [x] I have searched [github.com/aws/amazon-q-developer-cli/issues](https://github.com/aws/amazon-q-developer-cli/issues?q=) and there are no duplicates of my issue
- [x] I have run `q doctor` in the affected terminal session
- [x] I have run `q restart` and replicated the issue again

### Operating system

macos

### Expected behaviour

The /checkpoint command in q chat should initialize and create a checkpoint commit successfully, regardless of the user’s global Git GPG signing settings. Ideally, Q CLI should ignore global commit.gpgSign for its internal checkpoint commits or configure a local repo that does not require GPG signing.

### Actual behaviour

Running /checkpoint fails when global GPG signing is enabled, because the Q CLI uses the author Q which has no corresponding secret key. Git then fails to write the commit object.

Error output:
```
!> /checkpoint init

Failed to execute command: Checkpoints could not be initialized: Checkpoint operation failed: error: gpg failed to sign the data:
gpg: skipped "Q ": No secret key
[GNUPG:] INV_SGNR 9 Q
[GNUPG:] FAILURE sign 17
gpg: signing failed: No secret key

fatal: failed to write commit object
```

Additional notes:
- Workaround: Scope commit.gpgSign so it applies only to specific paths/repos, avoiding the Q CLI checkpoint repo.
- Suggestion: To prevent this class of issues, Q CLI could bundle its own Git binary and configuration, or ensure its internal checkpoint commits explicitly disable GPG signing (e.g., local repo config or -c commit.gpgSign=false when committing).

References:
- [aws/amazon-q-developer-cli issues](https://github.com/aws/amazon-q-developer-cli/issues)

### Steps to reproduce

1) Ensure the following global Git config exists:
```ini
[commit]
gpgSign = true
```
2) Open q chat.
3) Run /checkpoint.
4) Observe the failure with GPG signing and the “No secret key” error.

### Environment

```yaml
- OS: Darwin 24.6.0 (macOS)
- Shell: /bin/zsh
- Q CLI version: Unknown (not collected)
- Install method: Unknown (not collected)
- q diagnostic: Not collected
```