Volume Flyout feature

[unchihugo]

WIP volume control/mixer flyout, closes #26
"A standalone volume control flyout that expands into a volume mixer, replacing the default Windows volume flyout."

Other updates:

• turning on volume flyout fully hides the native W11 volume flyout (code partially derived from gpkgpk/HideVolumeOSD), unhides when turned back off or program closes
• updated how media players icons are cached, improving repeated media player data retrieval performance significantly
• added WindowHelper.IsMouseOverWindow for better mouseOver detection for volume flyout because WPF native implementation was spotty (ignores empty space, idle mouse) and replaced media flyout to use this as well - implement to all flyouts later
• Updated MainWindow.OpenAnimation to be able to place flyouts above each other & CloseAnimation to not necessarily need additional params anymore

Expanded flyout screenshots

Collapsed flyout

[Copilot]

Pull request overview

Implements a new Volume Flyout / Volume Mixer UI intended to replace the native Windows volume OSD, plus supporting settings, animations, and caching improvements.

Changes:

• Added a new VolumeMixerWindow (WPF flyout) with a master volume slider and expandable per-app session mixer.
• Integrated volume flyout triggering into the global keyboard hook and updated open/close animation plumbing to support stacking flyouts.
• Expanded settings + localization strings and updated media player icon caching utilities.

Reviewed changes

Copilot reviewed 24 out of 25 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
FluentFlyoutWPF/Windows/VolumeMixerWindow.xaml.cs	Implements volume flyout show/hide behavior, OSD hide/restore, and expand/collapse animations.
FluentFlyoutWPF/Windows/VolumeMixerWindow.xaml	Defines the volume flyout UI (master volume + expandable session list).
FluentFlyoutWPF/Windows/LockWindow.xaml.cs	Updates calls to OpenAnimation/CloseAnimation after signature changes.
FluentFlyoutWPF/ViewModels/VolumeMixerViewModel.cs	Adds view model for master volume + enumerating per-app audio sessions.
FluentFlyoutWPF/ViewModels/UserSettings.cs	Adds settings for volume flyout/mixer and premium-gated highlight option.
FluentFlyoutWPF/SettingsWindow.xaml	Adds navigation entry for the new Volume Flyout settings page and adjusts ordering.
FluentFlyoutWPF/Resources/Localization/Dictionary-en-US.xaml	Adds English strings for Volume Flyout/Mixer UI and premium perk text.
FluentFlyoutWPF/Pages/VolumeMixerPage.xaml.cs	Adds settings page code-behind and premium unlock handler.
FluentFlyoutWPF/Pages/VolumeMixerPage.xaml	Adds Volume Flyout/Mixer settings UI (toggles + duration).
FluentFlyoutWPF/Pages/HomePage.xaml.cs	Adds navigation handler to Volume Flyout page.
FluentFlyoutWPF/Pages/HomePage.xaml	Adds Volume Flyout card to the home dashboard and reflows grid layout.
FluentFlyoutWPF/Models/AudioSessionModel.cs	Introduces model for a single audio session (volume/mute/state/icon).
FluentFlyoutWPF/MainWindow.xaml.cs	Hooks volume flyout into keyboard events, syncs mouse-over across flyouts, updates media icon caching call, and updates animation helpers.
FluentFlyoutWPF/FluentFlyout.csproj	Adds the volume flyout demo image as content.
FluentFlyoutWPF/Classes/WindowHelper.cs	Adds IsMouseOverWindow Win32-based hit testing helper.
FluentFlyoutWPF/Classes/WindowBlurHelper.cs	Adds acrylic blur settings mapping for VolumeMixerWindow.
FluentFlyoutWPF/Classes/Utils/VolumeToSpeakerSymbolConverter.cs	Adds converter to choose speaker icon based on volume.
FluentFlyoutWPF/Classes/Utils/NullToVisibilityConverter.cs	Adds converter to toggle visibility based on null values (icons).
FluentFlyoutWPF/Classes/Utils/MediaPlayerData.cs	Refactors caching and adds PID-based icon caching for better performance.
FluentFlyoutWPF/Classes/Utils/DecimalPercentageToFullConverter.cs	Adds converter to display volume scalar as percentage.
FluentFlyoutWPF/Classes/Utils/BoolToAccentBrushConverter.cs	Adds converter to highlight active sessions using accent brush (premium setting).
FluentFlyoutWPF/Classes/NativeMethods.cs	Adds Win32 constants and ShowWindow P/Invoke for hiding/restoring native OSD.
FluentFlyoutWPF/Classes/AudioDeviceMonitor.cs	Modifies audio device monitoring implementation (currently removes notifications wiring).
FluentFlyoutWPF/App.xaml	Adds a new app-wide converter resource for opacity behavior.

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[Copilot]

SyncFromDevice() doesn't update the session State, so IsActive (and the active-app highlight) becomes stale after initial enumeration. Consider syncing _sessionControl.State into the State property here, and ensure IsActive raises change notifications when State changes.