feat(window): add default inner padding to Window body

Window children rendered flush against the frame, so content (settings
rows, placeholder text) touched the left edge. Wrap children in
.modern-sk-window-body with 16px padding for consistent breathing room.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/window/index.tsx

@@ -21,6 +21,6 @@ export const Window = ({
         </div>
       )}
     </div>
-    {children}
+    <div className="modern-sk-window-body">{children}</div>
   </div>
 );