feat: Refactor promotion handling to use UCI notation and improve move validation

modules/rule/src/main/scala/de/nowchess/rules/sets/DefaultRules.scala

@@ -455,13 +455,21 @@ object DefaultRules extends RuleSet:
 
   // ── Insufficient material ──────────────────────────────────────────
 
+  private def squareColor(sq: Square): Int = (sq.file.ordinal + sq.rank.ordinal) % 2
+
   private def insufficientMaterial(board: Board): Boolean =
-    val pieces = board.pieces.values.toList.filter(_.pieceType != PieceType.King)
-    pieces match
-      case Nil                                                                           => true
-      case List(p) if p.pieceType == PieceType.Bishop || p.pieceType == PieceType.Knight => true
-      case List(p1, p2)
+    val nonKings = board.pieces.toList.filter(_._2.pieceType != PieceType.King)
+    nonKings match
+      case Nil => true
+      case List((_, p)) if p.pieceType == PieceType.Bishop || p.pieceType == PieceType.Knight => true
+      case List((sq1, p1), (sq2, p2))
           if p1.pieceType == PieceType.Bishop && p2.pieceType == PieceType.Bishop
-            && p1.color != p2.color =>
+            && p1.color != p2.color
+            && squareColor(sq1) == squareColor(sq2) =>
+        true
+      case bishops
+          if bishops.forall(_._2.pieceType == PieceType.Bishop)
+            && bishops.map(_._2.color).distinct.size == 1
+            && bishops.map(e => squareColor(e._1)).distinct.size == 1 =>
         true
       case _ => false