fix(frontend): prevent body OverlayScrollbar from intercepting message list scroll events

The body-level OverlayScrollbar (position: fixed, z-index: 99999) with
clickScroll and dragScroll enabled was capturing pointer events on the
scrollbar track, preventing the message list's native scrollbar from
receiving them. Disable both interactions on the body instance since it
does not need to scroll.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/overlay-scrollbars-init.tsx

@@ -10,7 +10,7 @@ export function OverlayScrollbarsInit() {
       scrollbars: {
         theme: "os-theme-codeg",
         autoHide: "leave",
-        clickScroll: true,
+        dragScroll: false,
       },
       overflow: { x: "hidden" },
     },
@@ -22,4 +22,4 @@ export function OverlayScrollbarsInit() {
   }, [init])
 
   return null
-}
+}