feat(web): add Knowledge Graph link to navigation sidebar (SSC-11)

Add Knowledge Graph navigation item with Network icon to main nav

Author: Sakeeb91

apps/web/src/components/layout/sidebar.tsx

@@ -18,6 +18,7 @@ import {
   Search,
   LogOut,
   User,
+  Network,
 } from "lucide-react";
 import { cn } from "@/lib/utils";
 import { Button } from "@/components/ui/button";
@@ -72,6 +73,11 @@ const mainNavItems: NavItem[] = [
     href: "/quizzes",
     icon: ClipboardList,
   },
+  {
+    title: "Knowledge Graph",
+    href: "/knowledge-graph",
+    icon: Network,
+  },
   {
     title: "Study Guides",
     href: "/guides",