Add basic frontend: sidebar, views and inventory table

frontend/src/App.tsx

@@ -0,0 +1,32 @@
+import { useState } from 'react';
+import './App.css';
+import { TopologyView } from './pages/TopologyView';
+import { InventoryView } from './pages/InventoryView';
+import { IPsView } from './pages/IPsView';
+import { DiscoveryJobsView } from './pages/DiscoveryJobsView';
+import type { ViewKey } from './types';
+
+export function App() {
+  const [current, setCurrent] = useState<ViewKey>('inventory');
+
+  const renderView = () => {
+    switch (current) {
+      case 'topology':
+        return <TopologyView />;
+      case 'inventory':
+        return <InventoryView />;
+      case 'ips':
+        return <IPsView />;
+      case 'discovery':
+        return <DiscoveryJobsView />;
+      default:
+        return <InventoryView />;
+    }
+  };
+
+  return (
+    <>
+      {renderView()}
+    </>
+  );
+}