feat(immersive): add GPU blur + noise distortion in shader

- Multi-sample blur: 12 samples in circular pattern
- Noise-based UV distortion to break up pixelation
- Random sample offsets for organic blur effect
- All blur computation is GPU-side (no CPU cost)

src/lib/immersive/shaders/ambient.frag

@@ -2,59 +2,101 @@
 /**
  * Ambient Motion Fragment Shader
  *
- * Adds subtle GPU-driven motion to the background:
+ * Adds GPU-driven motion and blur simulation to the background:
+ * - Multi-sample blur (samples multiple nearby points)
  * - UV drift (slow wandering)
  * - Zoom oscillation (breathing effect)
  * - Color breathing (subtle brightness pulsing)
- *
- * All effects are controlled by u_intensity (0 = static, 1 = full motion).
- * All computation is GPU-side - no CPU per-frame work.
+ * - Noise-based distortion to break up pixelation
  */
 
 precision mediump float;
 
-// Input from vertex shader
 in vec2 v_texCoord;
-
-// Output
 out vec4 fragColor;
 
-// Uniforms
 uniform sampler2D u_texture;
-uniform float u_time;          // Time in seconds
-uniform float u_intensity;     // Motion intensity (0.0 - 1.0)
+uniform float u_time;
+uniform float u_intensity;
 
-// Constants for motion parameters - made MORE visible
-const float DRIFT_SPEED_X = 0.15;
-const float DRIFT_SPEED_Y = 0.12;
-const float DRIFT_AMOUNT = 0.08;  // 8% UV drift
+// Motion parameters
+const float DRIFT_SPEED_X = 0.12;
+const float DRIFT_SPEED_Y = 0.09;
+const float DRIFT_AMOUNT = 0.06;
 
-const float ZOOM_SPEED = 0.1;
-const float ZOOM_AMOUNT = 0.05;   // 5% zoom oscillation
+const float ZOOM_SPEED = 0.08;
+const float ZOOM_AMOUNT = 0.04;
 
-const float BREATH_SPEED = 0.2;
-const float BREATH_AMOUNT = 0.12; // 12% brightness pulse
+const float BREATH_SPEED = 0.15;
+const float BREATH_AMOUNT = 0.08;
+
+// Blur simulation parameters
+const float BLUR_RADIUS = 0.015;  // UV space blur radius
+const int BLUR_SAMPLES = 12;      // Number of samples for blur
+
+// Simple pseudo-random function
+float random(vec2 st) {
+    return fract(sin(dot(st.xy, vec2(12.9898, 78.233))) * 43758.5453123);
+}
+
+// Smooth noise function
+float noise(vec2 st) {
+    vec2 i = floor(st);
+    vec2 f = fract(st);
+
+    float a = random(i);
+    float b = random(i + vec2(1.0, 0.0));
+    float c = random(i + vec2(0.0, 1.0));
+    float d = random(i + vec2(1.0, 1.0));
+
+    vec2 u = f * f * (3.0 - 2.0 * f);
+
+    return mix(a, b, u.x) + (c - a) * u.y * (1.0 - u.x) + (d - b) * u.x * u.y;
+}
 
 void main() {
     vec2 uv = v_texCoord;
     vec2 center = vec2(0.5);
 
-    // UV drift - slow wandering motion
+    // UV drift
     float driftX = sin(u_time * DRIFT_SPEED_X) * DRIFT_AMOUNT * u_intensity;
     float driftY = cos(u_time * DRIFT_SPEED_Y * 1.3) * DRIFT_AMOUNT * u_intensity;
     uv += vec2(driftX, driftY);
 
-    // Zoom oscillation - subtle breathing
+    // Zoom oscillation
     float zoom = 1.0 + sin(u_time * ZOOM_SPEED) * ZOOM_AMOUNT * u_intensity;
     uv = center + (uv - center) / zoom;
 
-    // Clamp UV to avoid edge artifacts
-    uv = clamp(uv, 0.0, 1.0);
+    // Add subtle noise-based distortion to break up pixelation
+    float noiseScale = 8.0;
+    float distortAmount = 0.008;
+    float n1 = noise(uv * noiseScale + u_time * 0.1);
+    float n2 = noise(uv * noiseScale + 100.0 + u_time * 0.1);
+    uv += vec2(n1 - 0.5, n2 - 0.5) * distortAmount;
 
-    // Sample texture
-    vec4 color = texture(u_texture, uv);
+    // Multi-sample blur to smooth out the texture
+    vec4 color = vec4(0.0);
+    float totalWeight = 0.0;
 
-    // Color breathing - subtle brightness pulsing
+    for (int i = 0; i < BLUR_SAMPLES; i++) {
+        float angle = float(i) * 6.28318530718 / float(BLUR_SAMPLES);
+        float r = BLUR_RADIUS * (0.5 + 0.5 * random(uv + float(i)));
+        vec2 offset = vec2(cos(angle), sin(angle)) * r;
+
+        vec2 sampleUV = clamp(uv + offset, 0.0, 1.0);
+        float weight = 1.0 - length(offset) / BLUR_RADIUS;
+
+        color += texture(u_texture, sampleUV) * weight;
+        totalWeight += weight;
+    }
+
+    // Add center sample with higher weight
+    color += texture(u_texture, clamp(uv, 0.0, 1.0)) * 2.0;
+    totalWeight += 2.0;
+
+    color /= totalWeight;
+
+    // Color breathing
     float breath = 1.0 + sin(u_time * BREATH_SPEED) * BREATH_AMOUNT * u_intensity;
     color.rgb *= breath;