fix(agent-skills): hide callout on mobile viewports

No value in showing the agent prompt on small screens where users
aren't using coding agents.

Co-Authored-By: Claude <[email protected]>

Author: HazAT

src/components/agentSkillsCallout/style.module.scss

@@ -5,6 +5,10 @@
   border: 1px solid color-mix(in srgb, var(--accent-purple), transparent 60%);
   background: color-mix(in srgb, var(--accent-purple), transparent 92%);
   color: var(--gray-500);
+
+  @media (max-width: 768px) {
+    display: none;
+  }
 }
 
 :global(.dark) .wrapper {