Use pasted Booking.com search URL to pin scrape destination

The location_search_url column existed but was dead — the scraper always
rebuilt the URL from the free-text location name. Now the Location
Configuration form takes a "Booking.com search URL" field: paste the
address-bar URL from a real search and the scraper lifts ss/dest_id/
dest_type from it (the most reliable destination pin). Falls back to
dest_id, then plain name. Server also extracts dest_id from the URL for
the column and derives a display name from ss when none is typed.

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

backend/services/booking_scraper.py

@@ -333,6 +333,7 @@ async def scrape_date(
         adults=config['adults'],
         pages=config['pages_to_scrape'],
         dest_id=config.get('dest_id'),
+        search_url=config.get('location_search_url'),
     )
 
     if result.blocked: