fix(dashboard): clear API-unreachable warning when API recovers

Always call display() for the warning element so Observable Framework
replaces it on each poll re-run. Previously the conditional display()
call left the warning rendered indefinitely once shown.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

dashboard/src/index.md

@@ -149,7 +149,7 @@ if (_h1) { _h1.style.position = "relative"; withDocHelp(_h1, "/docs/overview");
 ```
 
 ```js
-if (summary.error) display(html`<div class="warning">⚠️ ${summary.error}</div>`);
+display(html`<div class="warning" style="display:${summary.error ? '' : 'none'}">⚠️ ${summary.error ?? ''}</div>`);
 ```
 
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