Fold tools/township_upload.py back into gen_township_fighters.py to match the
project's single-file convention. Odds generation, anti-arbitrage checks, ZIP
packing and the chunked upload now live alongside the other township helpers;
_best_variant reuses the existing _video_variants. Behaviour is unchanged.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>