- DB: elo column on user table (default 1200, added via ALTER TABLE IF NOT EXISTS)
- ELO calculated after every game save (K=32, min 100)
- Bots use their fixed ELO values; only human players' ELO changes
- AI page games save with bot name (e.g. 'Holzpferd Heinz') instead of 'Stockfish'
- User profile shows ELO badge below name
- Header shows current ELO for logged-in users (links to profile)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
