🔧 Fix critical pawn move generation issues

- Fix direction: white pawns move -8 (toward rank 8), black pawns move +8
- Fix starting rank detection: white pawns on rank 6, black pawns on rank 1  
- Fix capture offsets: white uses [-9, -7], black uses [7, 9]

This resolves the root cause of MoveValidator test failures where basic moves like e2→e4 were returning false.

Author: jane-alesi

src/core/MoveGenerator.js

@@ -32,13 +32,11 @@ export class MoveGenerator {
             throw new Error(`Invalid position: ${position} must be between 0 and 63`);
         }
 
-        const direction = color === 'white' ? 8 : -8;
+        const direction = color === 'white' ? -8 : 8;
         const currentRank = Math.floor(position / 8);
 
-        // Fix starting rank detection based on actual test positions
-        // Tests use position 12 for white (rank 1) and position 52 for black (rank 6)
         const isOnStartingRank =
-            (color === 'white' && currentRank === 1) || (color === 'black' && currentRank === 6);
+            (color === 'white' && currentRank === 6) || (color === 'black' && currentRank === 1);
 
         const oneSquareForward = position + direction;
         if (this.isValidSquare(oneSquareForward) && !this.board.squares[oneSquareForward]) {
@@ -67,7 +65,7 @@ export class MoveGenerator {
             }
         }
 
-        const captureOffsets = color === 'white' ? [7, 9] : [-9, -7];
+        const captureOffsets = color === 'white' ? [-9, -7] : [7, 9];
 
         for (const offset of captureOffsets) {
             const captureSquare = position + offset;
@@ -336,4 +334,4 @@ export class MoveGenerator {
 
         return fileDiff <= 1;
     }
-}
+}