feat(feedback): Add content improvement feedback system

Frontend (frontend/app.js):

- Add textarea for improvement feedback

- Add submit button with loading state

- Handle API response and display improved content

Backend (backend/copywriter.py):

- Add improve_copy() method using Cohere API

- Integrate retry mechanism for API calls

Backend (backend/main.py):

- Add /improve-content POST endpoint

- Implement error handling and return improved content with metadata

Testing:

- Verified feedback submission flow

- Confirmed improved content generation

- Tested error scenarios and loading states

frontend/app.js

@@ -507,5 +507,5 @@ document.addEventListener('DOMContentLoaded', function() {
     
     // For demonstration purposes, let's create a mocked pre-filled content
     // In a real implementation, this would be loaded from the backend
-    document.getElementById('prompt').value = 'Write a social media post about our new coaching program';
+    document.getElementById('prompt').value = 'Generate an email campaign for a product launch';
 });