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>

js/game/Board.js

@@ -63,9 +63,12 @@ export class Board {
      * @param {number} row - Row index (0-7)
      * @param {number} col - Column index (0-7)
      * @returns {Piece|null} Piece or null if empty
+     * @throws {Error} If position is out of bounds
      */
     getPiece(row, col) {
-        if (!this.isInBounds(row, col)) return null;
+        if (!this.isInBounds(row, col)) {
+            throw new Error(`Position (${row}, ${col}) is out of bounds`);
+        }
         return this.grid[row][col];
     }
 
@@ -91,11 +94,11 @@ export class Board {
      * @param {number} fromCol - Source column
      * @param {number} toRow - Destination row
      * @param {number} toCol - Destination column
-     * @returns {Piece|null} Captured piece if any
+     * @returns {Object} Result with captured piece
      */
     movePiece(fromRow, fromCol, toRow, toCol) {
         const piece = this.getPiece(fromRow, fromCol);
-        if (!piece) return null;
+        if (!piece) return { captured: null };
 
         const captured = this.getPiece(toRow, toCol);
 
@@ -106,7 +109,7 @@ export class Board {
         // Mark piece as moved
         piece.hasMoved = true;
 
-        return captured;
+        return { captured };
     }
 
     /**
@@ -184,7 +187,8 @@ export class Board {
     /**
      * Find king position for given color
      * @param {string} color - 'white' or 'black'
-     * @returns {Position|null} King position or null
+     * @returns {Position} King position
+     * @throws {Error} If king not found
      */
     findKing(color) {
         for (let row = 0; row < 8; row++) {
@@ -195,7 +199,7 @@ export class Board {
                 }
             }
         }
-        return null;
+        throw new Error(`${color} king not found on board`);
     }
 
     /**
@@ -217,4 +221,26 @@ export class Board {
 
         return pieces;
     }
+
+    /**
+     * Get all pieces on the board
+     * @param {string} color - Optional color filter
+     * @returns {Array<Piece>} Array of pieces
+     */
+    getAllPieces(color = null) {
+        if (color) {
+            return this.getPiecesByColor(color);
+        }
+
+        const pieces = [];
+        for (let row = 0; row < 8; row++) {
+            for (let col = 0; col < 8; col++) {
+                const piece = this.grid[row][col];
+                if (piece) {
+                    pieces.push(piece);
+                }
+            }
+        }
+        return pieces;
+    }
 }