Persist Peek volume setting across sessions

[ThanhNguyxn]

Summary of the Pull Request

This PR implements volume persistence for the Peek utility, addressing issue #31810. When users adjust the volume slider for audio or video files in Peek, the volume level is now remembered and applied to subsequent files across sessions.

PR Checklist

• [x] Closes #31810
• [x] Communication: I've discussed this with core contributors and this is an approved change
• [x] Tests: I have verified these changes work locally
• [x] Localization: No new localizable strings added
• [x] Documentation: Feature behavior follows existing UI patterns
• [x] Accessibility: Uses existing MediaPlayerElement transport controls

Detailed Description of the Pull Request / Additional comments

Implementation Details

The implementation follows the same pattern used for ConfirmFileDelete - a setting that can be modified directly by Peek and synced back to the settings file.

Changes:

1. Settings Layer (PeekProperties.cs):

   • Added MediaVolume as a DoubleProperty with default value of 1.0 (100%)

2. User Settings (IUserSettings.cs, UserSettings.cs):

   • Added MediaVolume property with getter/setter
   • Implemented save-to-settings logic that persists volume changes immediately
   • Added value clamping between 0.0 and 1.0

3. ViewModel (MainWindowViewModel.cs):

   • Added MediaVolume property that delegates to IUserSettings
   • Updated constructor to accept IUserSettings via DI

4. AudioControl (AudioControl.xaml.cs):

   • Added MediaVolumeProperty DependencyProperty
   • Added VolumeChanged event that fires when user changes volume via transport controls
   • Added volume tracking with _isSettingVolume flag to prevent recursive updates

5. FilePreview (FilePreview.xaml, FilePreview.xaml.cs):

   • Added MediaVolumeProperty DependencyProperty
   • Added MediaVolumeChanged event
   • Added ApplyMediaVolume() method that sets volume on both video and audio players
   • Subscribes to volume changes from both VideoPreview.MediaPlayer and AudioPreview

6. MainWindow (MainWindow.xaml, MainWindow.xaml.cs):

   • Added MediaVolume binding to FilePreview
   • Added MediaVolumeChanged event handler that updates ViewModel

How it works

1. When Peek loads, it reads the saved MediaVolume from settings
2. The volume flows from MainWindowViewModel → FilePreview → AudioControl/VideoPreview
3. When user adjusts volume via transport controls, the change bubbles up via events
4. MainWindowViewModel updates IUserSettings.MediaVolume, which saves to settings file
5. Next time Peek opens or a new file is previewed, the saved volume is applied

Validation Steps Performed

1. Open Peek with an audio file, adjust volume to 50%
2. Navigate to another audio file - volume should remain at 50%
3. Close and reopen Peek - volume should still be at 50%
4. Open a video file - volume should be at 50%
5. Adjust video volume to 75%
6. Open an audio file - volume should be at 75%

[ThanhNguyxn]

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