Dashboard: Update banner text (#6931)

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## PR-Codex overview
This PR updates the `label` prop of the `AnnouncementBannerUI` component to enhance the messaging about the Nebula App.

### Detailed summary
- Changed the `label` prop from "Nebula AI Beta is out and open to all" to "Announcing Nebula App — the most powerful AI for blockchains! Try it now!" in the `AnnouncementBannerUI` component.

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Author: MananTank

apps/dashboard/src/components/notices/AnnouncementBanner.tsx

@@ -48,7 +48,7 @@ export function AnnouncementBanner() {
   return (
     <AnnouncementBannerUI
       href="https://nebula.thirdweb.com/"
-      label="Nebula AI Beta is out and open to all"
+      label="Announcing Nebula App — the most powerful AI for blockchains! Try it now!"
       trackingLabel="nebula-beta-launch"
     />
   );