macOS: force surface layout sync in updateOSView (#12143)

`updateOSView` assumed SwiftUI always propagates frame changes to the
scroll view. Under system load, this can be deferred, leaving the
surface rendering at stale dimensions. Check for size mismatch and mark
layout as needed.


<img width="1408" height="464" alt="ghostty_bug"
src="https://github.com/user-attachments/assets/3a6f81ff-9d02-4ffa-aded-e2eddc9f40a5"
/>

---
AI Disclosure: Used Claude Code for PR preparation.

macos/Sources/Ghostty/Surface View/SurfaceView.swift

@@ -621,8 +621,13 @@ extension Ghostty {
         }
 
         func updateOSView(_ scrollView: SurfaceScrollView, context: Context) {
-            // Nothing to do: SwiftUI automatically updates the frame size, and
-            // SurfaceScrollView handles the rest in response to that
+            // SwiftUI may defer frame updates under system load (e.g., memory
+            // pressure, heavy I/O) or when external window managers trigger rapid
+            // layout changes. When that happens, the scroll view's bounds can
+            // fall out of sync with the size reported by GeometryReader, causing
+            // the surface to render at stale dimensions.
+            guard scrollView.bounds.size != size else { return }
+            scrollView.needsLayout = true
         }
         #else
         func makeOSView(context: Context) -> SurfaceView {