fix: prevent horizontal scrolling in sidebar nav (#14)

When overflow-y is set to auto, browsers implicitly set overflow-x to
auto as well, creating an unwanted horizontal scrollbar. Explicitly set
overflow-x-hidden on the sidebar nav element.

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

ui/goose2/src/features/sidebar/ui/Sidebar.tsx

@@ -171,7 +171,7 @@ export function Sidebar({
         </div>
 
         {/* Navigation (scrollable) */}
-        <nav className="flex-1 min-h-0 overflow-y-auto px-1.5 py-1">
+        <nav className="flex-1 min-h-0 overflow-y-auto overflow-x-hidden px-1.5 py-1">
           <div className="space-y-0.5">
             {/* New Chat */}
             <button