Cards: 3x2 front/back sprites, appearance overlays, flip via the Toggle menu

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/Decentralized.Domain/CardLook.cs

@@ -22,6 +22,16 @@ namespace Decentralized.Domain
 
         public const int Variants = 3;
 
+        /// <summary>五位数字，存在物品标签上：风扇、金手指、挡板、丝印、贴纸。</summary>
+        public string Encode() => $"{Fan}{Fingers}{Bracket}{Print}{Sticker}";
+
+        public static CardLook Decode(string s)
+        {
+            if (s == null || s.Length != 5) return default;
+            int D(int i) => Math.Max(0, Math.Min(Variants - 1, s[i] - '0'));
+            return new CardLook { Fan = D(0), Fingers = D(1), Bracket = D(2), Print = D(3), Sticker = D(4) };
+        }
+
         /// <summary>只在假卡上出现的取值：玩家一旦看到，就能肯定是假的。</summary>
         public bool HasFakeSign => Bracket == 2 || Print != 0 || Sticker == 1;