Link to Eurostar search page with pricing; add Bristol departures RTT link

Replace the Eurostar timetable link with the search URL
(eurostar.com/search/uk-en?adult=1&origin=…&destination=…&outbound=…)
so the footer links directly to the page that shows prices for the
specific date and destination.

Add a Bristol Temple Meads → Paddington departures link on RTT alongside
the existing Paddington arrivals link.

Also update "morning service unavailable" badge and tests to reflect the
removal of the morning-only cutoff filter from find_unreachable_morning_eurostars.

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

scraper/eurostar.py

@@ -48,6 +48,14 @@ def _slugify_station_name(name: str) -> str:
     return re.sub(r'[^a-z0-9]+', '-', name.lower()).strip('-')
 
 
+def search_url(destination: str, travel_date: str) -> str:
+    dest_id = DESTINATION_STATION_IDS[destination]
+    return (
+        f'https://www.eurostar.com/search/uk-en'
+        f'?adult=1&origin={ORIGIN_STATION_ID}&destination={dest_id}&outbound={travel_date}'
+    )
+
+
 def timetable_url(destination: str) -> str:
     dest_id = DESTINATION_STATION_IDS[destination]
     dest_slug = _slugify_station_name(destination)