[BUG] Plymouth ignores keymap due to missing vconsole / luks keymap issue

### Pre-flight checklist

- [x] I have searched existing issues and this is not a duplicate.
- [x] I have read the [Contributing Guidelines](https://github.com/CachyOS/linux-cachyos/blob/master/CONTRIBUTING.md).
- [x] I have verified the issue is reproducible with the latest available CachyOS kernel.
- [x] I have tried to reproduce the issue on Arch Linux's `linux` kernel.

### Upstream / vanilla kernel check

I have not tested with a vanilla/upstream kernel

### Kernel variant

linux-cachyos (EEVDF, Clang)

### System information (cachyos-bugreport.sh)

```text
https://paste.cachyos.org/p/f71b778.log
```

### Manual system information (if cachyos-bugreport.sh is unavailable)

```text

```

### Bug description

After updating today, my keymap was no longer recognized by plymouth luks password screen. It was falling back to en_US.

My update today:
[2026-05-31T14:00:19+0200] upgraded plymouth (24.004.60-14.1 -> 26.134.222-2.1)

I was able to fix it with:

I fixed it for me by adding /etc/vconsole.conf to initramfs:

```
sudo sed -i 's|^FILES=()|FILES=(/etc/vconsole.conf)|' /etc/mkinitcpio.conf
```

Then rebuild:
```
sudo mkinitcpio -P
```

### Steps to reproduce

Use a keymap, other than en-US.
Test on luks screen.

### Expected behavior

keymap is recognized

### Actual behavior

keymap is not recognized, fallback to en-US

### Logs / stack traces

```text

```

### Additional system information

_No response_