[BUG] SSH config writes wrong username for Shadeform instances — 'ubuntu' fails, 'shadeform' works

[dims]

Summary

After brev refresh, the SSH config contains two entries per Shadeform instance:

Host my-h100
  User ubuntu       ← wrong — causes Permission denied (publickey)

Host my-h100-host
  User shadeform    ← correct

All Brev docs say: ssh -F ~/.brev/ssh_config <instance-name>. Following that on a Shadeform instance fails:

ssh -F ~/.brev/ssh_config my-h100 "nvidia-smi"
ubuntu@69.19.137.94: Permission denied (publickey).

The working alias (my-h100-host) is not mentioned in docs, CLI output, or the create success message.

Why it is hard to debug

GCP instances work fine with the plain <name> alias (user ubuntu), so users with prior GCP experience have no reason to suspect the alias matters. The SSH config shows both aliases as equally valid. The Permission denied error looks like a key problem, not a username problem.

Steps to reproduce

1. Create a Hyperstack H100 instance
2. Run brev refresh
3. Run ssh -F ~/.brev/ssh_config <name> "nvidia-smi"
4. Observe: Permission denied (publickey)
5. Try ssh -F ~/.brev/ssh_config <name>-host "nvidia-smi" — succeeds

Suggested fix

Use the provider type to select the correct SSH username when generating the SSH config. Either remove the alias that uses the wrong username, or make the primary Host <name> entry always use the working username.

At minimum, print the correct SSH command in brev create output:

✓ my-h100 is ready
  SSH: ssh -F ~/.brev/ssh_config my-h100-host

CLI version: v0.6.316 | Provider: Hyperstack via Shadeform