feat: add SkSL GPU shaders for wallpaper animations

Ken Burns (zoom+pan), Color Shift (HSL cycling), Particles
(snow/rain/bokeh overlay), Vignette Pulse, Glitch (RGB split),
and Depth Parallax (gyroscope-driven 2.5D via depth map).

src/shaders/color-shift.ts

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+import { Skia } from "@shopify/react-native-skia";
+
+// Color Shift: cyclic hue/saturation breathing effect
+// Uniforms: time, intensity, speed
+export const colorShiftShader = Skia.RuntimeEffect.Make(`
+  uniform shader image;
+  uniform float2 resolution;
+  uniform float time;
+  uniform float intensity;
+  uniform float speed;
+
+  // RGB to HSL conversion
+  float3 rgb2hsl(float3 c) {
+    float mx = max(c.r, max(c.g, c.b));
+    float mn = min(c.r, min(c.g, c.b));
+    float l = (mx + mn) * 0.5;
+    float s = 0.0;
+    float h = 0.0;
+
+    if (mx != mn) {
+      float d = mx - mn;
+      s = l > 0.5 ? d / (2.0 - mx - mn) : d / (mx + mn);
+
+      if (mx == c.r) {
+        h = (c.g - c.b) / d + (c.g < c.b ? 6.0 : 0.0);
+      } else if (mx == c.g) {
+        h = (c.b - c.r) / d + 2.0;
+      } else {
+        h = (c.r - c.g) / d + 4.0;
+      }
+      h /= 6.0;
+    }
+
+    return float3(h, s, l);
+  }
+
+  float hue2rgb(float p, float q, float t) {
+    float tt = t;
+    if (tt < 0.0) tt += 1.0;
+    if (tt > 1.0) tt -= 1.0;
+    if (tt < 1.0/6.0) return p + (q - p) * 6.0 * tt;
+    if (tt < 1.0/2.0) return q;
+    if (tt < 2.0/3.0) return p + (q - p) * (2.0/3.0 - tt) * 6.0;
+    return p;
+  }
+
+  float3 hsl2rgb(float3 hsl) {
+    float h = hsl.x;
+    float s = hsl.y;
+    float l = hsl.z;
+
+    if (s == 0.0) return float3(l);
+
+    float q = l < 0.5 ? l * (1.0 + s) : l + s - l * s;
+    float p = 2.0 * l - q;
+
+    return float3(
+      hue2rgb(p, q, h + 1.0/3.0),
+      hue2rgb(p, q, h),
+      hue2rgb(p, q, h - 1.0/3.0)
+    );
+  }
+
+  half4 main(float2 coord) {
+    half4 color = image.eval(coord);
+    float3 hsl = rgb2hsl(float3(color.rgb));
+
+    float t = time * speed * 0.15;
+
+    // Shift hue cyclically
+    hsl.x = fract(hsl.x + intensity * 0.1 * sin(t));
+
+    // Pulse saturation
+    hsl.y = clamp(hsl.y + intensity * 0.15 * sin(t * 1.3), 0.0, 1.0);
+
+    // Subtle luminance breathing
+    hsl.z = clamp(hsl.z + intensity * 0.03 * sin(t * 0.8), 0.0, 1.0);
+
+    float3 rgb = hsl2rgb(hsl);
+    return half4(half3(rgb), color.a);
+  }
+`)!;