Scraper: don't flag not_listed from partial scrapes

A page-load timeout was logged and skipped, so a scrape could 'succeed'
with only page 1 of results — and the not_listed flagging then marked
every page-2 hotel absent, suppressing their last known rates.

- ScraperResult now tracks pages_requested/pages_ok
- scrape_date skips not_listed flagging when pages failed or when the
  scrape saw <60% of the date's 7-day coverage baseline; scraped rates
  are still saved, unseen hotels keep last known rate + scrape time

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/services/scraper_backends/base.py

@@ -59,6 +59,8 @@ class ScraperResult:
     rates: List[RateData] = field(default_factory=list)
     error_message: Optional[str] = None
     page_content_sample: Optional[str] = None  # For debugging
+    pages_requested: int = 0             # Result pages we set out to fetch
+    pages_ok: int = 0                    # Pages that loaded and parsed cleanly
 
 
 class ScraperBackend(ABC):