Add instance heartbeat settings sidebar

ui/src/components/InstanceSidebar.tsx

@@ -0,0 +1,21 @@
+import { Clock3, Settings } from "lucide-react";
+import { SidebarNavItem } from "./SidebarNavItem";
+
+export function InstanceSidebar() {
+  return (
+    <aside className="w-60 h-full min-h-0 border-r border-border bg-background flex flex-col">
+      <div className="flex items-center gap-2 px-3 h-12 shrink-0">
+        <Settings className="h-4 w-4 text-muted-foreground shrink-0 ml-1" />
+        <span className="flex-1 text-sm font-bold text-foreground truncate">
+          Instance Settings
+        </span>
+      </div>
+
+      <nav className="flex-1 min-h-0 overflow-y-auto scrollbar-auto-hide flex flex-col gap-4 px-3 py-2">
+        <div className="flex flex-col gap-0.5">
+          <SidebarNavItem to="/instance/settings" label="Heartbeats" icon={Clock3} />
+        </div>
+      </nav>
+    </aside>
+  );
+}