Make scroll-wheel volume changes configurable

[SetupCoding]

Summary

Makes all scroll-wheel volume adjustment behavior configurable via the Mouse Settings page, rather than always-on.

Settings

• Use scroll wheel in tray (existing, default: on) - scroll over the EarTrumpet tray icon to change volume
• Use global mouse wheel hook (existing, default: off) - scroll anywhere while the flyout is open to change volume
• Use scroll wheel in sliders (NEW, default: on) - scroll over individual volume sliders to change volume

Changes

• App.xaml.cs: Restore tray icon scroll handler, gated by UseScrollWheelInTray setting
• VolumeSlider.cs: Restore mouse wheel handler, gated by new UseScrollWheelInSliders setting
• FlyoutViewModel.cs: Restore MouseHook for global scroll, gated by UseGlobalMouseWheelHook setting
• AppSettings.cs: Add new UseScrollWheelInSliders property (default: true)
• EarTrumpetMouseSettingsPageViewModel.cs: Expose new setting to UI
• SettingsWindow.xaml: Add checkbox for new setting
• Resources.resx / Resources.Designer.cs: Add display string for new checkbox

All three scroll-wheel behaviors can now be independently toggled on or off by the user. Build succeeds with 0 errors.

[CLAassistant]

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2 out of 3 committers have signed the CLA.

✅ riverar
✅ SetupCoding
❌ actions-user
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