Add modern window context menu

[NNN (hellodda)]

Summary of the Pull Request

Replaces the legacy Win32 system menu with a modern XAML-based WindowContextMenu implementation (MenuFlyout). This enables the title bar context menu to fully adapt to the application's XAML theme (Dark/Light mode) while maintaining full backward compatibility with native system commands.

References and Relevant Issues

• Related to / Closes Title Bar Context Menu to match Dark Mode #14751

Detailed Description of the Pull Request / Additional comments

Key Implementation Details:

• XAML MenuFlyout Integration: Created WindowContextMenu inheriting from MenuFlyout to replace the legacy Win32 popup menu with modern UI/UX matching the application theme.
• Win32 Message Hooking via Subclassing: Attached a window subclass procedure (SetWindowSubclass) to intercept WM_CONTEXTMENU, WM_NCRBUTTONUP, WM_NCRBUTTONDOWN, WM_STYLECHANGED, and WM_SIZE messages.
• DPI & Coordinate Calculation: Converts screen coordinates from Win32 physical pixels to DPI-aware logical coordinates using GetDpiForWindow. Handles keyboard invocation (Shift+F10 / Apps key with (X: -1, Y: -1) coordinates) by automatically centering the menu relative to the parent window.
• Win32 Localization & Fallback: Queries localized strings dynamically from GetSystemMenu via GetMenuItemInfoW and strips accelerator keys (& escaping and \t shortcut strings) so text renders cleanly in XAML.
• Dynamic Menu Item Extensions: Detects and appends custom menu items inserted into HMENU by third-party window managers or extensions.
• State Management & Command Routing: Automatically toggles item enable/visibility states based on window style (WS_THICKFRAME) and state (SIZE_MAXIMIZED). Maps click events back to native WM_SYSCOMMAND messages (SC_RESTORE, SC_MOVE, SC_SIZE, SC_MINIMIZE, SC_MAXIMIZE, SC_CLOSE).

Validation Steps Performed

1. Theme Adaptation: Verified that right-clicking the window caption/titlebar renders a XAML context menu using the active application theme (Dark and Light modes).
2. System Commands: Verified that clicking Restore, Move, Size, Minimize, Maximize, and Close correctly dispatches WM_SYSCOMMAND to the host window.
3. DPI Scaling: Tested menu popup positioning across high-DPI displays (125%, 150%, 200%) and multi-monitor setups.
4. Keyboard Invocation: Pressed Shift+F10 and the Apps key to verify the menu centers correctly on screen without crashing or rendering off-screen.
5. Window State Sync: Verified menu items automatically enable/disable when switching between windowed and maximized states.

PR Checklist

• Closes Title Bar Context Menu to match Dark Mode #14751
• Tests added/passed
• Documentation updated
• Schema updated (if necessary)

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[NNN (hellodda)]

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