Getting horizontal gradient in unlit sprite shader even sprite is rotated

Hello,

I am writing a basic unlit sprite shader that creates gradient between 2 colors. I achieved that easily with lerping the value with UV's y coordinate. But with that way, when I rotate my sprite, gradient is rotating with sprite, as expected. Lerping the value with pixel's world space position's y value solved rotation problem, but only if sprite is at the center of the world. When sprite is moved to different position in world, gradient value is changing. I want to achieve gradient is horizontal all the time and only happening inside sprite boundaries. How can write that with using fragment shader?

Current state of my shader:

 Shader "Custom/SpriteGradient"
 {
      Properties
      {
          _MainTex ("Main Texture", 2D) = "white" {}
          _TopColor ("Top Color", Color) = (1, 1, 1, 1)
          _BottomColor ("Bottom Color", Color) = (1, 1, 1, 1)
          [Toggle(BLEND)] _Blend("Blend With Texture", Float) = 0
      }
      SubShader
      {
          Pass
          {
              Blend SrcAlpha OneMinusSrcAlpha
              CGPROGRAM
              #pragma vertex vert
              #pragma fragment frag
              #pragma shader_feature BLEND
              #include "UnityCG.cginc"
 
              struct vertexIn {
                  float4 pos : POSITION;
                  float2 uv : TEXCOORD0;
              };
 
              struct v2f {
                  float4 pos : SV_POSITION;
                  float2 uv : TEXCOORD0;
              };
 
 
              fixed4 _TopColor, _BottomColor;
              sampler2D _MainTex;
              fixed4 _MainTex_ST;
              float4x4 _TextureRotation;
 
              v2f vert(vertexIn input)
              {
                  v2f output;
                  output.pos = UnityObjectToClipPos(input.pos);
                  output.uv = input.uv;
                  output.worldPos = mul (unity_ObjectToWorld, input.pos);
                  output.screenPos = ComputeScreenPos(input.pos);
                  return output;
              }
 
 
              fixed4 frag(v2f input) : COLOR
              {
                 float2 screenUV = input.screenPos.xy / input.screenPos.w;
                 //float currentY = input.worldPos.y;
                 //float4 centerY = mul(unity_ObjectToWorld, float4(0.5,0.5,0.0,1.0)).y;
 
                 fixed4 textureColor = tex2D(_MainTex, input.uv);
                 fixed4 gradientValue = lerp(_BottomColor, _TopColor, input.uv.y);
                 textureColor.rgb *= textureColor.a;
 
                 #ifdef BLEND
                     textureColor.rgb *= gradientValue;
                 #else
                     textureColor.rgb = gradientValue.rgb;
                 #endif
 
                 return textureColor;
              }
              ENDCG
          }
      }
 }
 

This is the state where I get graient value by using UV.y . Actually, finding center position is easy. If there is some built-in function that can give world position of the highest and lowest pixel position at Y axis correctly (even sprite is rotated upside down), I guess I can lerp using those values.

Any help would be greatly appreciated. I am new to shader coding.

Thank you all.