Refactor farm building speed to builder unit action_speeds and enable infinite charges

shaders/simple.frag

@@ -11,6 +11,11 @@ uniform sampler2D texTundra;  // Unit 8 (Texturelabs_Soil_135XL tundra soil)
 uniform sampler2D texRedSand; // Unit 9 (Texturelabs_RedSand prairie sand)
 uniform sampler2D texRedRock; // Unit 10 (Texturelabs_RedRock canyon cliff)
 uniform sampler2D texForest;  // Unit 11 (Texturelabs_Forest_seamless woodland floor)
+uniform sampler2D texFarm;    // Unit 12 (images/farm.jpeg)
+
+uniform int isFarm;
+uniform float farmTextureScale;
+uniform int farmMappingMode;
 
 uniform float time;
 uniform int riverMask;
@@ -213,6 +218,22 @@ void main() {
                      + tundraColor  * tundraWeight
                      + redSandColor * prairieWeight;
 
+    // Farm improvement texture applied when a farm is present
+    if (isFarm == 1) {
+        float scale = max(0.01, farmTextureScale);
+        vec2 farmUV;
+        if (farmMappingMode == 1) {
+            // Hex-centered mapping with aspect ratio correction
+            vec2 centered = vec2(tilePos.x - 0.5, (tilePos.y - 0.4328799) * 1.154734411);
+            farmUV = centered * scale + vec2(0.5, 0.5);
+        } else {
+            // World-space coordinates: perfectly seamless and continuous across adjacent hex tiles
+            farmUV = vWorldPos.xy * scale;
+        }
+        vec4 farmColor = texture(texFarm, farmUV);
+        biomeGround = farmColor;
+    }
+
     // Shoreline beach: where gentle slopes meet water (sea level up to ~110m, or along rivers)
     // Steep slopes (norm.z < 0.55) remain rocky cliffs; gentle slopes (norm.z > 0.80) get a sandy beach
     float gentleSlope = smoothstep(0.55, 0.85, norm.z);