Closes#9
Previously SEASON_PCT was hardcoded to 81/162 (~0.5) while END_DATE was
set to 20050731 (~65% through the season). Running retrosheet_data.py
directly (without the CLI which overrides SEASON_PCT at runtime) would
silently generate cards using half-season normalizations on stats covering
a larger portion of the season.
Fix: move START_DATE/END_DATE before SEASON_PCT and derive SEASON_PCT
from the date range using SEASON_END_DATE (2005 regular season end).
Now changing END_DATE automatically produces the correct SEASON_PCT.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>