`krun.use_passt=1` fails without `--userns auto`

## Environment

- Host: Fedora, x86_64
- Runtime:
```
rpm -q podman crun passt
podman-6.1.0-1.fc45.x86_64
crun-1.29.1-1.fc45.x86_64
passt-0^20260728.gf8df3f1-2.fc45.x86_64
```
- Image: `alpine:latest`

## Symptom

```text
sudo podman --log-level debug run -it --rm \
--annotation krun.use_passt=1 \
--annotation run.oci.handler=krun \
--name test alpine:latest
```

Fails with:

```text
Error: OCI runtime error: crun: failed configuring mounts for handler at phase: HANDLER_CONFIGURE_AFTER_MOUNTS: start passt
```

Adding `--userns auto` makes the same command succeed.
## Suggested workaround

- Keep `--userns auto` for krun containers that use `krun.use_passt=1`.

Reproduce the reported Podman command with and without --userns auto, then trace the krun.use_passt=1 annotation through crun’s passt startup and mount-configuration path. Done means the command succeeds without --userns auto and the regression is covered by a test for the reported setup.

Written by the indexing model from the issue text.