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

data/past_campaigns/case_study_20240101.json

@@ -0,0 +1,16 @@
+{
+  "content": "From Overwhelmed to Outstanding: How Sarah Thompson Transformed Her Consulting Business\n\nThe Challenge:\nSarah Thompson built a successful consulting business but hit a plateau. Working 60+ hours weekly, she struggled with:\n• Inconsistent revenue\n• No scalable systems\n• Constant decision fatigue\n\nThe Solution:\nThrough the Business Evolution Program, Sarah implemented:\n1. Strategic Decision Framework\n2. Revenue Optimization System\n3. Team Empowerment Protocol\n4. Client Acquisition Blueprint\n\nThe Results:\n• Revenue increased 127% in 90 days\n• Work hours reduced to 35/week\n• Client satisfaction up 45%\n• Team efficiency improved 85%\n\nIn Sarah's Words:\n\"The framework transformed not just my business, but how I think about success. I now have clear systems, confident decision-making, and sustainable growth.\"\n\nYour Turn:\nReady to write your success story? Book your strategy session now.",
+  "content_type": "case_study",
+  "metadata": {
+    "campaign_name": "Client Success Stories",
+    "performance_metrics": {
+      "read_completion_rate": 0.72,
+      "lead_generation_rate": 0.18,
+      "sharing_rate": 0.25
+    },
+    "added_at": "2024-01-01T00:00:00Z",
+    "training_data": true
+  },
+  "document_id": 8,
+  "timestamp": "2024-01-01T00:00:00Z"
+}