feat: add configurable removedCells option and comprehensive documentation

- Add removedCells to GameOptions for custom puzzle sizes
- removedCells overrides difficulty default when provided
- Maintain backward compatibility with all defaults
- Complete IMPLEMENTATION.md with Iteration 16 and summary
- Completely rewrite README.md with comprehensive documentation:
  - Complete API reference (GameOptions, GameManager, CursorManager, ScoreManager)
  - Game states and state machine flow
  - Full VIM controls reference (movement, editing, hints, game control)
  - Cell state rules and visual feedback
  - Detailed scoring formula with examples
  - Game-over conditions (time and hint limits)
  - Hint system priority and penalties
  - Configuration examples for different play styles
  - Platform hook integration guide
- Mark implementation as COMPLETE and PRODUCTION READY

src/useGame.ts

@@ -7,7 +7,7 @@ import { useCursorRender } from './useCursor/useCursorRender';
 import { useScore } from './useScore';
 
 export function useGame(options: GameOptions = {}, platformHook?: unknown): GameManager {
-  const { difficulty = 'easy', timeLimit = 600 } = options;
+  const { difficulty = 'easy', timeLimit = 600, removedCells } = options;
   const board = useBoard();
   const { containerRef, renderBoard, generateBoard, boardRendered } = board;
   
@@ -51,12 +51,12 @@ export function useGame(options: GameOptions = {}, platformHook?: unknown): Game
 
   useEffect(() => {
     if (gameStatus === 'started') {
-      generateBoard(difficulty);
+      generateBoard(difficulty, removedCells);
       renderBoard();
     } else if (gameStatus === 'waiting') {
       renderBoard();
     }
-  }, [gameStatus, difficulty]);
+  }, [gameStatus, difficulty, removedCells]);
 
   const gameManager: GameManager = {
     containerRef,