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/social_media_20240101.json

@@ -0,0 +1,16 @@
+{
+  "content": "Stop waiting for permission to succeed.\n\nYour business breakthrough isn't about luck – it's about strategy.\n\nIn just 60 minutes, discover:\n→ The exact framework for consistent growth\n→ How to eliminate decision paralysis\n→ Your unique success blueprint\n\nJoin the free masterclass: [Link in bio]\n\nTag a business owner who needs to hear this 👇\n\n#BusinessSuccess #Leadership #BusinessStrategy #Growth",
+  "content_type": "social_media",
+  "metadata": {
+    "campaign_name": "Masterclass Promotion",
+    "performance_metrics": {
+      "engagement_rate": 0.35,
+      "reach": 15000,
+      "saves": 245
+    },
+    "added_at": "2024-01-01T00:00:00Z",
+    "training_data": true
+  },
+  "document_id": 3,
+  "timestamp": "2024-01-01T00:00:00Z"
+}