Git hook messages aren't displayed

The stack CLI suppresses git hook output, which is confusing when the hooks are slow and frustrating when the hooks fail. For example, a `gh stack push` that fails because of a hook just outputs

```
❯ gh stack push
Skipping 1 merged branch
Pushing 2 branches to origin...
✗ failed to push: failed to run git: error: failed to push some refs to 'github.com:...'
```

Start by reproducing the issue with `gh stack push` and a Git hook that is slow or fails, then trace how the stack CLI runs Git commands and handles their output. Done means hook messages are visible during the command and hook failures retain useful output while still reporting the push failure.

Written by the indexing model from the issue text.