data: refresh custom_ids with Understat competition/team/season IDs

Added 147 Understat mappings from Kaggle dataset:
- 6 competitions, 100 teams, 41 seasons (Big 5 + RFPL)

Total custom_ids: 353,266 → 353,413

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: rahulkeerthi