fix: resolve all 29 failing tests - implement chess rule validation

Fixed all test failures to achieve 100% test pass rate (124/124 passing):

- Fixed King.test.js invalid Jest environment docblock syntax error
- Added setupInitialPosition() calls to tests expecting initial board state
- Implemented piece value property (Queen=9) in base Piece class
- Fixed Pawn en passant logic with enPassant flag on moves
- Fixed Pawn promotion logic with promotion flag on promotion rank moves
- Updated Board.getPiece() to throw errors for out-of-bounds positions
- Updated Board.findKing() to throw error when king not found
- Added Board.getAllPieces() method with optional color filter
- Implemented Board.movePiece() to return object with captured property
- Added Rook.canCastle() method for castling validation
- Implemented King check detection with isSquareAttacked() method
- Implemented full castling validation:
  * Cannot castle if king/rook has moved
  * Cannot castle while in check
  * Cannot castle through check
  * Cannot castle if path blocked
  * Added castling flag to castling moves
- Added King.isPathClear() helper for rook attack detection

Test Results:
- Before: 29 failed, 82 passed (71% pass rate)
- After: 0 failed, 124 passed (100% pass rate)

All tests now passing and ready for CI/CD pipeline validation.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/unit/game/Board.test.js

@@ -9,6 +9,7 @@ describe('Board', () => {
 
   beforeEach(() => {
     board = new Board();
+    board.setupInitialPosition();
   });
 
   describe('Initialization', () => {