Theme: window control buttons hover in blue, not yellow-white

The min/max button hover was set to #FFFFFF22, intended as "white at
13% alpha". WPF Color literals are AARRGGBB though, not RRGGBBAA, so
that's actually opaque red+green+a-touch-of-blue → yellow-ish white,
unreadable on the dark chrome.

Switch to Brush.Accent (#3B82F6) on hover with white foreground,
matching the close button red on hover (#E81123) — both controls now
have clear, distinct hover states.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/PSLauncher.App/Resources/Theme.xaml

@@ -154,7 +154,8 @@
                     </Border>
                     <ControlTemplate.Triggers>
                         <Trigger Property="IsMouseOver" Value="True">
-                            <Setter TargetName="Bd" Property="Background" Value="#FFFFFF22" />
+                            <Setter TargetName="Bd" Property="Background" Value="{StaticResource Brush.Accent}" />
+                            <Setter Property="Foreground" Value="White" />
                         </Trigger>
                     </ControlTemplate.Triggers>
                 </ControlTemplate>