High contrast themes

Problem

People with certain visual impairments may have difficulty using Fluxer using the built-in themes, even with the existing Accessibility settings.

Proposed solution

Have high contrast themes built into the Fluxer client as theming options.

Notes (optional)

WebAIM page on WCAG 2 contrast and colour requirements: https://webaim.org/articles/contrast/ Microsoft's high contrast guidelines: https://learn.microsoft.com/en-us/windows/apps/design/accessibility/high-contrast-themes Qt's high contrast themes across desktop OSes showing multiple examples of high contrast theming: https://www.qt.io/blog/high-contrast-mode-in-qt-6.10