Retry page load timeouts: treat as blocks, bump max retries to 4

DataImpulse endpoints are intermittently broken — some return EOF after
CONNECT immediately, others work fine. DNS round-robins between them so
the same request can fail 3× then succeed on the 4th. Timeouts were
returning blocked=False and silently failing with no retry. Now treated
as retryable blocks (with context rotation) so a fresh endpoint is tried.
Max retries 2→4 (5 total attempts) to give enough chances to land a
working DataImpulse endpoint.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/services/booking_scraper.py

@@ -318,7 +318,7 @@ async def scrape_hotel_date(
     backend: 'PlaywrightHotelPageBackend',
     batch_id: uuid.UUID,
     adults: int = 2,
-    max_retries: int = 2,
+    max_retries: int = 4,
 ) -> Dict[str, Any]:
     """
     Scrape all rate plans for one hotel on one date via the hotel page backend.