fix: SetWindowChrome ResizeBorderThickness for non-resizable modes

[xyliteee]

Pull request type

Please check the type of change your PR introduces:

• 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?

PR #1719 added a ResizeMode check in TitleBar.GetWindowBorderHitTestResult() to prevent resizing when ResizeMode is NoResize or CanMinimize. However, this was only a partial fix — the root cause is in FluentWindow.SetWindowChrome(), where ResizeBorderThickness is incorrectly set to 4 for CanMinimize mode.

Because WindowChrome handles WM_NCHITTEST independently of TitleBar's HwndSourceHook, the TitleBar fix alone cannot fully prevent resizing in CanMinimize mode. The window borders remain resizable via WindowChrome.ResizeBorderThickness.

Related: #1719

What is the new behavior?

• FluentWindow.SetWindowChrome() now only sets ResizeBorderThickness = 4 when ResizeMode is CanResize or CanResizeWithGrip
• CanMinimize and NoResize now correctly get ResizeBorderThickness = 0, preventing unintended window resizing at the WindowChrome level
• This is the proper fix for the issue addressed in fix: TitleBar respects ResizeMode.NoResize #1719

Other information

This PR supersedes / completes the fix started in #1719. The previous PR worked around the symptom in TitleBar; this PR fixes the root cause in FluentWindow.

Minimal repro XAML (before fix — window borders remain resizable):

<<ui:FluentWindow ResizeMode="CanMinimize" ExtendsContentIntoTitleBar="True">
    <ui:TitleBar/>
</ui:FluentWindow>