Update documentation for testing infrastructure

- Add test commands to CLAUDE.md and README.md
- Update file structure to include game-logic.js and __tests__/
- Document Jest test suite with 57 tests

CLAUDE.md

@@ -17,6 +17,12 @@ cd server && npm start
 # or
 cd server && node index.js
 
+# Run tests
+cd server && npm test
+
+# Run tests with coverage
+cd server && npm run test:coverage
+
 # Server runs on http://localhost:3000 (or PORT env variable)
 ```
 
@@ -24,11 +30,13 @@ cd server && node index.js
 
 ### Server-Client Model
 
-- **Server** (`server/index.js`): Express + Socket.io handles all game logic authoritatively
+- **Server** (`server/`): Express + Socket.io handles all game logic authoritatively
+  - `index.js`: Main server with socket.io event handlers
+  - `game-logic.js`: Pure game logic functions (testable, no socket dependencies)
+  - `__tests__/`: Jest test suite with 57 tests
   - Manages single global lobby with `lobby.players` Map
   - Game tick runs at 50ms intervals via `gameTick()`
   - Broadcasts state updates to all connected clients via `broadcastState()`
-  - Tetromino definitions and board constants are duplicated on server
 
 - **Client** (`public/js/`): Vanilla JavaScript with module pattern
   - `network.js`: Socket.io client wrapper, manages player/game state caching