topbar: surface publish warnings instead of discarding them

handlePublish's JSON response has always included a `warnings` array
(e.g. the contact-form relay's "submissions will not be delivered"
notice), but nothing in the editor ever read it. Adds a PublishWarnings
banner, held in its own state independent of the 3s publishStatus
flash so the customer has time to read it, rendered in both the
desktop and mobile TopBar branches.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

craft/src/panels/topbar/PublishWarnings.tsx

@@ -0,0 +1,31 @@
+import React from 'react';
+
+export interface PublishWarningsProps {
+  warnings: string[];
+  onDismiss: () => void;
+}
+
+/** Non-blocking banner shown after a successful publish. The site IS live --
+ *  these are things the customer should fix and re-publish, not failures. */
+export const PublishWarnings: React.FC<PublishWarningsProps> = ({ warnings, onDismiss }) => {
+  if (!warnings.length) return null;
+
+  return (
+    <div className="publish-warnings" role="status" data-testid="publish-warnings">
+      <i className="fa fa-exclamation-triangle" aria-hidden="true" />
+      <ul>
+        {warnings.map((w, i) => (
+          <li key={i}>{w}</li>
+        ))}
+      </ul>
+      <button
+        type="button"
+        onClick={onDismiss}
+        aria-label="Dismiss"
+        data-testid="publish-warnings-dismiss"
+      >
+        <i className="fa fa-times" aria-hidden="true" />
+      </button>
+    </div>
+  );
+};