feat: implement scoring system and win condition (Phase 50)

- Add useTimer hook for elapsed time tracking
- Add useScore hook with comprehensive metrics:
  - Total keystrokes (all keys)
  - Edit keystrokes (only editing keys)
  - Optimal keystrokes (empty cells × 3)
  - Efficiency percentage (optimal/edit × 100)
  - Final score (70% efficiency + 30% time-based)
- Win condition detects board completion only in normal mode
- Track all keystrokes with timestamps in useGame
- Update example app with full scoreboard display
- Expose boardRef in BoardManager for state checking
- Adjust easy mode to 5 removed cells for testing

src/types.ts

@@ -1,11 +1,13 @@
 import type { RefObject } from 'react';
 import type { GameStatus, GameStatusManager } from './useGameStatus/types';
 import type { CursorManager } from './useCursor/types';
+import type { ScoreManager } from './useScore/types';
 
 export type Difficulty = 'easy' | 'medium' | 'hard';
 
 export type { GameStatus, GameStatusManager };
 export type { CursorManager, Coord } from './useCursor/types';
+export type { ScoreManager } from './useScore/types';
 
 export type GameOptions = {
   difficulty?: Difficulty;
@@ -17,11 +19,7 @@ export type GameManager = {
   containerRef: RefObject<HTMLDivElement | null>;
   renderBoard: () => void;
   cursor: CursorManager;
-  scoreManager: {
-    timeValue: number;
-    keystrokes: number;
-    finalScore: number | null;
-  };
+  scoreManager: ScoreManager;
   keyLog: KeyLogEntry[];
   clearKeyLog: () => void;
   getKeyLog: () => KeyLogEntry[];