Add AI status badges to show verification status on prices

- Add ai_status column to price_history table (verified/corrected/null)
- Track AI verification status through scraper and scheduler
- Display badges next to prices:
  - ✓ AI (green): AI verified the price is correct
  - ⚡ AI (orange): AI corrected an incorrect price
- Show badges on Dashboard product cards and ProductDetail page
- Add legend explaining badges in Settings when AI Verification is enabled

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/routes/products.ts

@@ -65,7 +65,8 @@ router.post('/', async (req: AuthRequest, res: Response) => {
       await priceHistoryQueries.create(
         product.id,
         scrapedData.price.price,
-        scrapedData.price.currency
+        scrapedData.price.currency,
+        scrapedData.aiStatus
       );
     }