Add feature for cursor and range rings

shaders/ppi_targets.frag

@@ -0,0 +1,11 @@
+#version 330 core
+in vec2 vUV;         // [-1,1] range — distance from blob centre
+out vec4 fragColor;
+uniform vec3  uColor;
+uniform float uFalloff;  // gaussian width: larger = tighter core
+void main() {
+    float d = length(vUV);
+    if (d > 1.0) discard;
+    float intensity = exp(-uFalloff * d * d);
+    fragColor = vec4(uColor * intensity, intensity);
+}