WgpuMetalSurface_mac: switch to <AppKit/AppKit.h> umbrella

The narrow `<AppKit/NSView.h>` header only forward-declares NSWindow,
so `view.window.backingScaleFactor` fails to compile on macOS with:

    error: property 'backingScaleFactor' cannot be found in forward
           class object 'NSWindow'

Use the AppKit umbrella header so NSWindow's interface (including
backingScaleFactor) is in scope. Same idiomatic include any non-trivial
Cocoa code reaches for; we're already linking -framework Cocoa so
there's no compile-time cost beyond a slightly heavier translation
unit (the .mm is ~30 lines anyway).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ifcviewer-wgpu/WgpuMetalSurface_mac.mm

@@ -7,7 +7,10 @@
 
 #if defined(__APPLE__)
 
-#import <AppKit/NSView.h>
+// The AppKit umbrella header pulls in NSWindow so `view.window`'s
+// `backingScaleFactor` resolves — `<AppKit/NSView.h>` alone only
+// forward-declares NSWindow.
+#import <AppKit/AppKit.h>
 #import <QuartzCore/CAMetalLayer.h>
 
 void* wgpu_macos_attach_metal_layer(void* nsview_ptr) {