Fix Play/Pause button losing album art accent color on hover and press

[lgc2333]

Summary

Keep the album art accent color on the play/pause button in hover and pressed states instead of switching to the system accent shade.

Motivation

Closes #910. Supersedes #913.

Type of Change

• Feature
• Bug fix
• Refactor (no functional changes)
• Style (formatting, naming)
• Other

What Changed

• Added PlayPauseButtonStyle in MainWindow.xaml, based on MicaWPF.Styles.AccentedButton, keeping the same GradientBorder template but replacing the MouseOver/Pressed visual-state color animations with opacity triggers (IsMouseOver → 0.9, IsPressed → 0.8).
• ControlPlayPause now uses that style.

Additional Information

Root cause: the AccentedButton template animates ContentBorder.Background.Color to AccentFillColorSecondary/Tertiary in the MouseOver/Pressed visual states. Animations outrank the local Background set by UpdateUI, so the album art color only survived in the normal state — hover/press fell back to the system accent, and disabled used AccentFillColorDisabled.

Why not #913's approach: it replaces GradientBorder with a plain Border, losing the accent inner stroke and the Margin="-2" extension, so the button renders smaller and flatter than the other AccentedButtons; it also strips the file BOM and is based on stale code (already conflicting). This PR keeps the original template and only removes the color animation. The opacity values match Fluent's own accent hover/press fills (0.9/0.8), so hover intensity is unchanged; disabled keeps the album art color dimmed by the existing Opacity = 0.35.

Checklist

• Code changes are manually tested and working.
• Formatting and naming are consistent with the project.
• Self-review of changes is done.
• AI tools were used (if yes, I reviewed and fully understand the changes myself).

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[lgc2333]

I have read and agree to the FluentFlyout CLA

[lgc2333]

hi, @unchihugo , the CLA issue has not been resolved

[unchihugo]

Should be fixed now, sorry

Edit: ignore it for now!

[unchihugo]

Hi @lgc2333, could you make it so that opacity is only changed for the background? Currently, the symbol/icon is also adjusted, and is the reason why I couldn't merge the referenced PR either.

[lgc2333]

commited by agent hosted on cloud, haven't tested yet

[lgc2333]

hi, it's looking fine now

original behavior for comparing (using windows system accent):

[lgc2333]

hi, just a friendly reminder because there's no response for a while. review this if you have time :)

[unchihugo]

Hi @lgc2333, I don't have access to a PC right now, so could you show the same hover behaviors currently in master compared to your branch?

[lgc2333]

combine image 1, 5, 6, it's the original behavior

[lgc2333]

Bump for review. Anything blocking this?

[unchihugo]

Hi @lgc2333, I was busy. Will merge now!