fix: prevent sidebar wheel from blocking tree library scrolling

frontend/src/components/layout/Sidebar.tsx

@@ -112,8 +112,27 @@ export function Sidebar() {
     }
   }
 
+  const handleSidebarWheel = (e: React.WheelEvent<HTMLElement>) => {
+    const sidebar = e.currentTarget
+    const canSidebarScroll = sidebar.scrollHeight > sidebar.clientHeight
+    const atTop = sidebar.scrollTop <= 0
+    const atBottom = sidebar.scrollTop + sidebar.clientHeight >= sidebar.scrollHeight - 1
+
+    // If sidebar can't consume wheel movement, forward it to main content scroller.
+    if (!canSidebarScroll || (e.deltaY < 0 && atTop) || (e.deltaY > 0 && atBottom)) {
+      const main = document.querySelector('.main-content') as HTMLElement | null
+      if (main) {
+        main.scrollTop += e.deltaY
+        e.preventDefault()
+      }
+    }
+  }
+
   return (
-    <nav className="sidebar flex flex-col border-r border-border bg-[hsl(var(--sidebar-bg))]">
+    <nav
+      className="sidebar flex flex-col border-r border-border bg-[hsl(var(--sidebar-bg))]"
+      onWheel={handleSidebarWheel}
+    >
       {sidebarCollapsed ? (
         <>
           {/* Collapsed: icon-only nav */}