fix(ListView): use themed disabled background instead of SystemColors.ControlBrush

[apachezy]

Pull request type

Please check the type of change your PR introduces:

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the current behavior?

Problem The ListView with GridView template (GridViewTemplate) sets the disabled state background to SystemColors.ControlBrush, bypassing Wpf.Ui’s theme resource keys. In dark themes this produces a jarring white block while adjacent controls use dark palette values, breaking visual consistency.

Screenshot (Dark Theme):

Screenshot (Light Theme):

Changes made:

Updated the disabled state background in ListView's GridViewTemplate from SystemColors.ControlBrushKey to ControlFillColorDisabledBrush.

What is the new behavior?

Effects Disabled ListView with GridView now blends into the themed surface (light: subtle muted fill; dark: appropriate subdued dark tone) instead of defaulting to pure white.

Screenshot (Dark Theme):

Screenshot (Light Theme):

Other information

I believe a better approach would be to remove this trigger and not alter the background color for the disabled state at all. However, for now, this fix is scoped only to replacing the brush.

[apachezy]

I will close this PR due to a type conversion error.

[apachezy]

Reopening this PR as the issue was unrelated.

After further investigation, I've confirmed that the exception in my project was caused by an unrelated issue. This PR, which applies the themed disabled background, is correct and does not introduce any regressions.

The fix here is still valid and improves theme consistency. It is ready for review.