Port WPF desktop UI to built-in .NET Fluent theme

[Copilot]

• Verify current WPF desktop build before theming changes
• Inspect theme switching and remaining SystemColors/static color usage
• Replace SystemColors-based UI backgrounds/text/borders with Fluent dynamic resources so dark mode affects the full UI
• Add app-level styling for common controls to restore cleaner, original-inspired spacing, hierarchy, and accent usage
• Refine main window, certificate list, detail tabs, and flyout surfaces for consistent cards, borders, and selected states
• Remove conflicting local highlight/resource overrides that prevent theme propagation
• Rebuild the WPF desktop app and verify no MahApps/static resource regressions
• Run final validation

[CLAassistant]

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✅ webprofusion-chrisc
❌ Copilot
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[webprofusion-chrisc]

Button and tab theming needs to be close to native windows WinUI fluent design (attached is the lepo WPF ui version). IN particular buttons and tabs should be slightly rounded so lets reduce extra styling for control radius. Let's minimize custom styling but keep our accented color theme for light and dark