Add bot to play against.

README.md

@@ -1,7 +1,8 @@
 # Super Auto Pets: The Board Game — Online
 
 A web app for playing the Super Auto Pets board game remotely. 1v1 for now;
-the engine is built to grow to more players.
+the engine is built to grow to more players. Play a friend by room code, or
+play solo against a computer opponent (easy / medium / hard).
 
 ## Stack
 
@@ -94,8 +95,22 @@ All six tiers use the real card data:
 ```
 cmd/server/          entrypoint
 internal/game/       rules engine (pure, fully tested)
-internal/server/     HTTP + WebSocket rooms
+internal/ai/         computer opponent (decides from a player View only)
+internal/server/     HTTP + WebSocket rooms; drives bot turns
 internal/store/      SQLite persistence
 internal/env/        .env loading
 web/                 React frontend
 ```
+
+## The computer opponent
+
+Any seat can be a bot (`Player.IsBot`); humans and bots are interchangeable
+to the engine, which is what will let future >2-player games mix them
+freely. The AI in `internal/ai` never touches the `Game` — it decides from a
+`game.View`, the same per-player state a human client is sent, plus a
+persisted memory of public observations (battle lineups, the event log, shop
+row changes). It cannot see your deck order, hidden trade picks, or the
+shuffled shop decks. It scores candidate moves by Monte-Carlo battle
+rollouts (`game.SimulateBattle`) against sampled guesses of your deck and
+ordering, blended with a long-term deck-value heuristic; difficulty tunes a
+softmax over the scored moves plus the rollout budget.