```

feat(gameplay): 实现护盾系统和强化增益选择机制

- 新增护盾功能，包括护盾数值显示和护盾条UI
- 重构盾卫技能，实现坚固壁垒技能效果
- 添加暴击率、吸血率等战斗属性
- 优化增益选择界面，新增传奇品质和刷新机制
- 调整材质纹理和文字着色器效果
- 修复金币显示格式问题
```

Assets/Shader/UIGoldText.shader

@@ -5,8 +5,10 @@ Shader "UI/GoldTextGradient"
         [PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
         _Color ("Tint", Color) = (1,1,1,1)
 
-        _TopColor ("Top Gold Color", Color) = (1, 0.95, 0.6, 1)
-        _BottomColor ("Bottom Gold Color", Color) = (0.9, 0.65, 0.1, 1)
+        _TopColor ("Top Color (White)", Color) = (1.0, 0.98, 0.95, 1.0)
+        _MiddleColor ("Middle Color (Light Gold)", Color) = (1.0, 0.82, 0.4, 1.0)
+        _BottomColor ("Bottom Color (Amber Gold)", Color) = (0.82, 0.5, 0.1, 1.0)
+        _MidPoint ("Gradient Mid Point", Range(0.1, 0.9)) = 0.35
 
         _StencilComp ("Stencil Comparison", Float) = 8
         _Stencil ("Stencil ID", Float) = 0
@@ -68,9 +70,12 @@ Shader "UI/GoldTextGradient"
 
             fixed4 _Color;
             fixed4 _TopColor;
+            fixed4 _MiddleColor;
             fixed4 _BottomColor;
+            float _MidPoint;
             sampler2D _MainTex;
             float4 _MainTex_ST;
+            fixed4 _TextureSampleAdd;
 
             v2f vert(appdata_t IN)
             {
@@ -79,7 +84,19 @@ Shader "UI/GoldTextGradient"
                 OUT.vertex = UnityObjectToClipPos(OUT.worldPosition);
                 OUT.texcoord = TRANSFORM_TEX(IN.texcoord, _MainTex);
                 
-                fixed4 gradColor = lerp(_BottomColor, _TopColor, saturate(IN.texcoord.y));
+                float y = saturate(IN.texcoord.y);
+                fixed4 gradColor;
+                if (y > _MidPoint)
+                {
+                    float t = (y - _MidPoint) / (1.0 - _MidPoint);
+                    gradColor = lerp(_MiddleColor, _TopColor, t);
+                }
+                else
+                {
+                    float t = y / _MidPoint;
+                    gradColor = lerp(_BottomColor, _MiddleColor, t);
+                }
+
                 OUT.color = IN.color * _Color * gradColor;
                 return OUT;
             }