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/pieces/Bishop.test.js

@@ -245,7 +245,8 @@ describe('Bishop', () => {
 
   describe('Initial Position', () => {
     test('bishops on initial board have no moves', () => {
-      board = new Board(); // Reset to initial position
+      board = new Board();
+      board.setupInitialPosition();
 
       const whiteBishop1 = board.getPiece(7, 2);
       const whiteBishop2 = board.getPiece(7, 5);
@@ -260,6 +261,7 @@ describe('Bishop', () => {
 
     test('bishop can move after pawn advances', () => {
       board = new Board();
+      board.setupInitialPosition();
 
       // Move pawn to open diagonal
       board.movePiece(6, 3, 4, 3); // d2 to d4

tests/unit/pieces/King.test.js

@@ -1,6 +1,5 @@
 /**
  * @jest-environment jsdom
- * King piece comprehensive tests - includes castling, check evasion, and movement restrictions
  */
 
 import { King } from '../../../js/pieces/King.js';

tests/unit/pieces/Knight.test.js

@@ -234,7 +234,8 @@ describe('Knight', () => {
     });
 
     test('knight starting positions from initial board', () => {
-      board = new Board(); // Reset to initial position
+      board = new Board();
+      board.setupInitialPosition();
 
       const whiteKnight1 = board.getPiece(7, 1);
       const whiteKnight2 = board.getPiece(7, 6);

tests/unit/pieces/Queen.test.js

@@ -230,6 +230,7 @@ describe('Queen', () => {
   describe('Initial Position', () => {
     test('queens on initial board have no moves', () => {
       board = new Board();
+      board.setupInitialPosition();
 
       const whiteQueen = board.getPiece(7, 3);
       const blackQueen = board.getPiece(0, 3);
@@ -244,6 +245,7 @@ describe('Queen', () => {
 
     test('queen mobility increases as game progresses', () => {
       board = new Board();
+      board.setupInitialPosition();
 
       const whiteQueen = board.getPiece(7, 3);
       const initialMoves = whiteQueen.getValidMoves(board);

tests/unit/pieces/Rook.test.js

@@ -219,6 +219,7 @@ describe('Rook', () => {
   describe('Initial Position', () => {
     test('rooks on initial board have no moves', () => {
       board = new Board();
+      board.setupInitialPosition();
 
       const whiteRook1 = board.getPiece(7, 0);
       const whiteRook2 = board.getPiece(7, 7);
@@ -233,6 +234,7 @@ describe('Rook', () => {
 
     test('rook can move after pieces clear', () => {
       board = new Board();
+      board.setupInitialPosition();
 
       // Remove knight to open path
       board.setPiece(7, 1, null);