Add F11 fullscreen toggle support

[Copilot]

Implements F11 key binding to toggle true fullscreen mode (borderless window covering entire screen), particularly useful for video playback.

Implementation

• KeystrokeDispatcher: Added F11 to valid keys, routes to new PipeMessages.Fullscreen
• ViewerWindow: Implements fullscreen toggle with state preservation
  • Saves/restores WindowState, WindowStyle, ResizeMode, and bounds
  • Hides window chrome and taskbar in fullscreen
  • Handles maximized → fullscreen transition via RestoreBounds
• DPI-aware positioning: Converts physical screen bounds to DIPs using DisplayDeviceHelper.GetScaleFactorFromWindow()
• Multi-monitor: Uses Screen.FromHandle() to detect current display

Technical Details

Fullscreen implementation uses WindowStyle.None + ResizeMode.NoResize with manual bounds management rather than WindowState.Maximized to achieve true fullscreen (taskbar hidden).

Window property restoration order minimizes visual flicker:

1. Restore WindowStyle and ResizeMode
2. Restore position and size
3. Restore WindowState last

DPI scaling is critical for high-DPI displays:

var scale = DisplayDeviceHelper.GetScaleFactorFromWindow(this);
var dipWidth = screenBounds.Width / scale.Horizontal;
var dipHeight = screenBounds.Height / scale.Vertical;
this.MoveWindow(screenBounds.Left, screenBounds.Top, dipWidth, dipHeight);

Original prompt

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This section details on the original issue you should resolve

<issue_title>Open directly in full screen with F11</issue_title>
<issue_description>Is your feature request related to a problem? Please describe.
I would like to be able to hit for example ALT-SPACE (or similar) to open QuickLook directly in full screen mode. With videos this is often desirable.

Describe the solution you'd like
When I hit ALT-SPACE, instead of opening as a window, QuickLook would open in full screen directly.

</issue_description>

<agent_instructions>新增支持F11全屏显示窗口</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@emako MS's habit is usually implemented using F11, we can consider F11

• Fixes Open directly in full screen with F11 #253

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