Add tfl_fare.py with circle_line_fare() which returns £3.10 (peak) or
£3.00 (off-peak) based on TfL Zone 1 pricing. Peak applies Monday–Friday
(excluding England public holidays) 06:30–09:30 and 16:00–19:00.
Annotate each circle service with its fare in trip_planner.py, display
it alongside the Circle line times in the Transfer column, and include
it in the journey Total.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
