Add cheapest_gwr_ticket() to trip_planner.py encoding the SSS/SVS/SDS
walk-on single restrictions for Bristol Temple Meads → Paddington: on
weekdays, Super Off-Peak (£45) is valid before 05:05 or from 09:58,
Off-Peak (£63.60) from 08:26, and Anytime (£138.70) covers the gap.
Weekends have no restrictions. The fare is included in each trip dict
and displayed in a new GWR Fare column on the results page.
Also wire up find_unreachable_morning_eurostars() into the results view
so early Eurostar services unreachable from Bristol appear in the table,
with tests covering both features.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
