Enable Vulkan encoding for wlroots capture method.

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### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your issue described in the documentation?

- [x] I have read the documentation

### Is your issue present in the latest beta/pre-release?

This issue is present in the latest pre-release

### Describe the Bug

Hi! #5030 disabled vulkan encoding for the wlroots capture method

> "AMD+wlr+vulkan worked, but it broke NVIDIA+wlr+nvenc — "buffer formats (linear, non-linear) break wlr screencopy,"

Recently we've had a fix regarding wlroots: #5699

I was wondering if that's enough to maybe get vulkan enabled for wlroots again, or if there's still more work needed to be done. I have an AMD gpu only, so I can't test it with nvidia to see if it's still broken.

This would be a nice to have because flatpak installs can't do the CAP_SYS_NICE changes while using vaapi, which could cause the encoder to throttle if host GPU usage is high. An issue completely avoided by vulkan encode.

### Expected Behavior

Be able to use Vulkan encode with wlroots capture method.

### Additional Context

_No response_

### Host Operating System

Linux

### Operating System Version

Aurora (Version: 44.20260915.1)

### Architecture

amd64/x86_64

### Package

Linux - flathub/flatpak

### GPU Type

AMD

### GPU Model

RX 6700 XT

### GPU Driver/Mesa Version

Mesa 26.2.2

### Capture Method

wlroots (FreeBSD/Linux)

### Apps

```json

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### Log output

```shell

```

### Online logs

_No response_

Start by reviewing the changes referenced in #5030 and the wlroots fix in #5699, then trace the wlroots capture and Vulkan encoding paths. Done means Vulkan encoding can be selected with wlroots while preserving NVIDIA/wlroots/NVENC compatibility; hardware testing on both AMD and NVIDIA is needed.

Written by the indexing model from the issue text.