feat: prepare vim-sudoku for unified API implementation

- Archive previous implementation attempt (src -> src_failed)
- Create comprehensive IMPLEMENTATION_PLAN.md with phased approach
- Create IMPLEMENTATION.md to track implementation progress
- Update example app to match vim-maze patterns:
  - Simplify UI to desktop-only (no mobile support)
  - Add score metrics display (time, keystrokes, final score)
  - Update instructions for sudoku-specific keys (hjkl, i for edit)
  - Remove unnecessary mobile hooks

Phase 5 complete. Ready to begin Phase 10 (Setup & Core Types).

src_failed/useGameStatus/useGameStatus.ts

@@ -0,0 +1,32 @@
+import { useState, useCallback } from 'react';
+import type { GameStatusManager, GameStatus } from './types';
+
+export function useGameStatus(): GameStatusManager {
+  const [gameStatus, setGameStatus] = useState<GameStatus>('waiting');
+
+  const startGame = useCallback(() => {
+    setGameStatus('started');
+  }, []);
+
+  const togglePause = useCallback((pause?: boolean) => {
+    setGameStatus(current => {
+      if (current === 'started' || current === 'paused') {
+        return pause !== undefined ? (pause ? 'paused' : 'started') : 
+               (current === 'started' ? 'paused' : 'started');
+      }
+      return current;
+    });
+  }, []);
+
+  const quitGame = useCallback(() => {
+    setGameStatus('waiting');
+  }, []);
+
+  return {
+    gameStatus,
+    setGameStatus,
+    startGame,
+    togglePause,
+    quitGame
+  };
+}