style: add scrollbar-gutter to prevent layout shift

- Implement `scrollbar-gutter: stable` in global CSS
- Prevent layout shifts when scrollbar appears or disappears

src/styles/globals.css

@@ -50,6 +50,11 @@
 }
 
 @layer base {
+  html {
+    /* prevent the layout from shifting when the scrollbar appears or disappears. */
+    scrollbar-gutter: stable;
+  }
+  
   * {
     @apply border-border outline-ring/50;
   }