fix(33): add subtle prominence to Revert AI Changes button

Use neutral-300 text, neutral-700/50 bg, and neutral-600 border
to make the button noticeable without clashing with the app style.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/components/Header.tsx

@@ -371,7 +371,7 @@ export function Header() {
           {previousWorkflowSnapshot && (
             <button
               onClick={handleRevertAIChanges}
-              className="px-2.5 py-1.5 text-xs text-neutral-400 hover:text-neutral-200 hover:bg-neutral-800 rounded transition-colors"
+              className="px-2.5 py-1.5 text-xs text-neutral-300 hover:text-neutral-100 bg-neutral-700/50 hover:bg-neutral-700 border border-neutral-600 rounded transition-colors"
               title="Restore workflow from before AI changes"
             >
               Revert AI Changes