[Bug]: openat(O_CREAT) on bind mount fails when file mode lacks owner-read bit

### I have done the following

- [x] I have searched the existing issues
- [ ] If possible, I've reproduced the issue using the 'main' branch of this project

### Steps to reproduce

When a non-root process creates a file on a bind-mounted host directory, `openat(O_WRONLY|O_CREAT, mode)` returns `EACCES` if the mode lacks the owner-read bit (`0400`). The same call succeeds on the container's native filesystem.

## Reproducer

```bash
mkdir /tmp/virtiofs-repro

container run --rm --user 1000:1000 -v /tmp/virtiofs-repro:/mnt alpine sh -c '
apk add --no-cache python3 > /dev/null 2>&1
mkdir /mnt/test

python3 -c "
import os
d = \"/mnt/test\"

# Works: mode includes owner-read
fd = os.open(d + \"/ok\", os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o600)
os.close(fd)
print(\"mode 0600 (rw-------): OK\")

# Fails: mode lacks owner-read
try:
fd = os.open(d + \"/fail\", os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o200)
os.close(fd)
print(\"mode 0200 (-w-------): OK\")
except PermissionError:
print(\"mode 0200 (-w-------): FAILED\")

# Control: same call on native filesystem works
os.makedirs(\"/tmp/native\", exist_ok=True)
fd = os.open(\"/tmp/native/ok\", os.O_WRONLY | os.O_CREAT | os.O_TRUNC, 0o200)
os.close(fd)
print(\"mode 0200 on native fs: OK\")
"'

rm -rf /tmp/virtiofs-repro
```

## Impact

This breaks C++ `std::filesystem::copy`, which internally creates destination files with `openat(O_WRONLY|O_CREAT|O_TRUNC, 0200)`. In my case, [Nix](https://nixos.org/) package manager builds fail because of this.

The key line in GCC's libstdc++ is here: https://github.com/gcc-mirror/gcc/blob/4eef89cc39a629988453e964258374cd7a047b1f/libstdc%2B%2B-v3/src/filesystem/ops-common.h#L553

## Related issues

- [containers/podman#24725](https://github.com/containers/podman/issues/24725) — same underlying virtiofs bug, reported as `mkdirat(., ., 0)` failing with EACCES on vfkit macOS. References Apple feedback ticket **FB16008360**.
- [docker/for-mac#6812](https://github.com/docker/for-mac/issues/6812) — virtiofs maps file permissions incorrectly on macOS
- [crc-org/vfkit#70](https://github.com/crc-org/vfkit/issues/70) — APFS-backed virtiofs permission issues

### Current behavior

```
mode 0600 (rw-------): OK
mode 0200 (-w-------): FAILED
mode 0200 on native fs: OK
```

### Expected behavior

```
Mode 0600 (rw-------): OK
mode 0200 (-w-------): OK
mode 0200 on native fs: OK
```

### Environment

```markdown
- OS: macOS 26.3.1 (a) (25D771280a)
- Xcode:
- Container: 0.10.0
```

### Relevant log output

```shell
N/A
```

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

Start by running the provided container and Python reproducer on macOS, then search the repository for the openat, O_CREAT, and virtiofs handling involved in bind-mounted files. Compare the bind-mounted and native-filesystem results; done means mode 0200 creation succeeds for a non-root process and the relevant tests pass.

Written by the indexing model from the issue text.