fix(web): tool-call checkmarks nearly invisible on the terracotta (light) theme

text-success/50 and /60 washed out to almost nothing against the light
theme's cream card background — full-opacity text-success still reads
as a calm, muted green (not alarming) but is actually visible on both
themes.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/lib/components/ToolCallCard.svelte

@@ -14,7 +14,7 @@
   const statusColor = $derived.by(() => {
     if (status === 'running') return 'text-primary'
     if (status === 'error') return 'text-destructive'
-    return 'text-success/60'
+    return 'text-success'
   })
 
   const argsSummary = $derived.by(() => {