fix: Improved duplicate prevention in cast iron scanner

- Better link normalization and checking
- Skip items already in seen_links with logging
- Clean up state file to last 500 items
- Always mark items as seen (deal or not)
- Added logging for skipped duplicates

Also: eBay scraping temporarily blocked/changed - investigating

agents/sales-lead/state.json

@@ -1,7 +1,7 @@
 {
   "processed_leads": [],
   "processed_calc_ids": [1, 2, 3, 4],
-  "last_check": "2026-04-10T15:18:09Z",
+  "last_check": "2026-04-10T20:00:01Z",
   "status": "active",
   "notes": "Hourly monitoring enabled. Next check in 60 minutes."
 }