AI seats were saved with no engine id, so the ladder filed every model
as full-strength Stockfish and dropped model-vs-model matches as
self-play. Rate each model at a help level and effort as its own player,
with its spend per game, and show them in an AI ladder.

The picker now lists each provider's newest current chat models from
Prompture's catalogue, with prices, key status and the efforts each
model supports, instead of two hardcoded tiles.