feat: add timeLimit option and time-based game-over logic

- Add timeLimit to GameOptions (default 600 seconds)
- Game-over triggers when time limit exceeded
- Remove all efficiency-based game-over logic
- Pass timeLimit through to useScore
- Check time limit during started and has-key states

src/types.ts

@@ -11,6 +11,7 @@ export * from './useScore/types';
 export type GameOptions = {
   rows: number;
   cols: number;
+  timeLimit?: number;
 };
 
 export type KeyLogEntry = { key: string; timestamp: number };