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/sales_copy_20240101.json

@@ -0,0 +1,16 @@
+{
+  "content": "Introducing the Business Evolution Program\n\nTransform your business in 90 days.\n\nYou've built a business. Now it's time to build your legacy.\n\nThe Business Evolution Program gives you:\n\n✓ Proven 7-figure business framework\n✓ Weekly strategic mentoring sessions\n✓ Custom growth roadmap\n✓ High-performance tools suite\n✓ Private client network access\n\nInvestment: $5,997\nEarly Decision Bonus: VIP Strategy Day ($2,000 value)\n\nOnly 15 spots available for Q1 2024.\n\nSchedule your private consultation now and receive your custom business analysis ($500 value) - no cost, no obligation.\n\nTake action now → [Book Consultation]\n\nYour future self will thank you for making this decision today.",
+  "content_type": "sales_copy",
+  "metadata": {
+    "campaign_name": "Q1 Program Launch",
+    "performance_metrics": {
+      "conversion_rate": 0.12,
+      "average_order_value": 5997,
+      "consultation_booking_rate": 0.35
+    },
+    "added_at": "2024-01-01T00:00:00Z",
+    "training_data": true
+  },
+  "document_id": 5,
+  "timestamp": "2024-01-01T00:00:00Z"
+}