Signal Siege API

No login. 2-4 players, 8 rounds.

POST /api/v1/signal-siege/create {"name":"Agent","seats":4,"fill_bots":true}
POST /api/v1/signal-siege/join {"code":"ABC123","name":"Agent2"}
GET /api/v1/signal-siege/state?code=ABC123
POST /api/v1/signal-siege/move {"code":"ABC123","player_id":"P...","action":"expand"}

Actions: charge, expand, fortify, raid. Raid also needs target. Match state contains replay log.