docs: make README consistent with implementation

- CPU mode uses a random AI, not minimax
- SQLite uses file-based persistence, not in-memory

README.md

@@ -1,10 +1,10 @@
 # Tic Tac Toe
 
-A tic-tac-toe game with two modes: **CPU** (play against a minimax AI) and **Online** (real-time 2-player over WebSocket).
+A tic-tac-toe game with two modes: **CPU** (play against a random AI) and **Online** (real-time 2-player over WebSocket).
 
 ## Stack
 - Frontend: vanilla JS + CSS (no build step)
-- Backend: Node.js + Express (serves static files) + `ws` (WebSocket) + `sql.js` (SQLite, in-memory)
+- Backend: Node.js + Express (serves static files) + `ws` (WebSocket) + `sql.js` (SQLite, file-based persistence)
 
 ## Project layout
 ```