feat: Add testimonials and update Gemini model

Integrates a testimonial system to display user results and feedback. This includes:
- Adding a new `testimonials` collection in Firestore.
- Implementing frontend components for displaying and submitting testimonials.
- Modifying the Gemini service to use the `gemini-3.1-pro-preview` model for enhanced analysis.
- Updating the `PlansView` with a new WhatsApp contact number.
- Enhancing the `AdminDashboard` to include testimonial creation capabilities.

src/components/PlansView.tsx

@@ -143,7 +143,7 @@ export const PlansView: React.FC<PlansViewProps> = ({ isUnauthenticated, onGetSt
       onGetStarted();
     } else {
       // Handle payment or subscription logic for logged in users
-      window.open('https://wa.me/258840000000?text=Ol%C3%A1%2C%20gostaria%20de%20assinar%20o%20plano%20do%20QuantScan', '_blank');
+      window.open('https://wa.me/258869976193?text=Ol%C3%A1%2C%20gostaria%20de%20assinar%20o%20plano%20do%20QuantScan', '_blank');
     }
   };