phase-2: extract shared utils

ui/src/lib/MarketContext.svelte

@@ -1,7 +1,10 @@
 <script>
+  import { untrack } from 'svelte';
+
   let { ctx, collapsible = false } = $props();
 
-  let expanded = $state(!collapsible);  // collapsed by default when collapsible=true
+  // Read collapsible once for initial state — untrack avoids a reactive dep on the prop
+  let expanded = $state(untrack(() => !collapsible));
 
   const cards = $derived.by(() => {
     const b = ctx?.benchmarks ?? {};