Fetching from an unknown remote host causes the fetch task to hang

### Describe the bug
When fetching from a remote host that is not present in known_hosts, the fetch task gets stuck indefinitely instead of failing or prompting for host verification.

This usually happens on first contact with a new SSH remote.

### To Reproduce
1. Ensure the remote host is not present in ~/.ssh/known_hosts
2. Configure a repository with an SSH remote pointing to that host
3. Run the fetch shortcut
4. Observe that the fetch task never completes

### Expected behavior
The fetch operation should:
- Prompt for SSH host verification or
- Fail with a clear error indicating the host is unknown or
- implicitly accept new host

### Version info:

commit=v0.58.1, build date=2026-01-12T20:22:34Z, build source=binaryRelease, version=0.58.1, os=linux, arch=amd64, git version=2.52.0

### Terminal info:
Ghostty 1.2.3-arch2