Fix total_pages calculation bug and add tests

- Fixed total_pages calculation: API returns 5 events/page, not PAGE_SIZE
- This was causing partial=false positives when max_total was used
- Updated tests to use correct pagination values

skills/polymarket-browse/scripts/browse.py

@@ -235,7 +235,7 @@ def fetch_all_pages(
     if total_raw == 0:
         return {"events": [], "total_raw": 0, "partial": False}
 
-    total_pages = (total_raw + PAGE_SIZE - 1) // PAGE_SIZE
+    total_pages = (total_raw + 4) // 5
     concurrency = min(MAX_PARALLEL_FETCHES, total_pages)
 
     all_page_data: dict[int, list[Any]] = {}