Fix: ResizeMode="NoResize" ignored in FluentWindow after PR #1560

[Copilot]

PR #1560 introduced TitleBar.WindowResize.cs for border resize hit-testing, but did not guard against ResizeMode="NoResize" or ResizeMode="CanMinimize". The Math.Max(2, …) floor in the DPI helpers ensured the border hit zone was always ≥2px — overriding FluentWindow.SetWindowChrome()'s ResizeBorderThickness = default — so windows remained draggable regardless of ResizeMode.

Pull request type

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the current behavior?

Setting ResizeMode="NoResize" or ResizeMode="CanMinimize" on a FluentWindow has no effect — the window edges still show resize cursors and can be dragged to resize.

What is the new behavior?

• GetWindowBorderHitTestResult checks the parent window's ResizeMode before performing any border hit-testing.
• If ResizeMode is NoResize or CanMinimize, it returns HTNOWHERE immediately, suppressing resize cursors and drag-resize entirely.

private IntPtr GetWindowBorderHitTestResult(IntPtr hwnd, IntPtr lParam)
{
    if (
        _parentWindow is Window parentWindow
        && parentWindow.ResizeMode is ResizeMode.NoResize or ResizeMode.CanMinimize
    )
    {
        return (IntPtr)PInvoke.HTNOWHERE;
    }
    // ...
}

Other information

Regression introduced by #1560.

[chucker]

6250edc fixes it for Wpf.Ui.Controls.MessageBox and for an example roughly like the one in #1691.

However, in TitleBar, the maximize button still works, and shouldn't.