fix: amplify ambient shader motion for visible animation

Previous shader was too subtle — drift, rotation, and breathing were
imperceptible with the smooth 8x8 texture. Now with much larger values:
- Drift: 0.05 -> 0.20 max (Lissajous with two frequencies)
- Scale breathing: 2% -> 12% range
- Rotation: 0.86deg -> 5deg range
- Added warm/cool color shifting over time
- Stronger vignette pulsing and brightness breathing

Safe because the 8x8-sourced texture has zero structure to reveal.

src/lib/immersive/shaders/ambient.frag

@@ -2,10 +2,9 @@
 /**
  * Ambient Immersion Shader
  *
- * Single-layer approach with slow drift, rotation, and breathing.
- * Produces smooth organic motion without multi-layer blending artifacts.
- * The pre-blurred texture does all the heavy lifting — the shader just
- * adds gentle life to it.
+ * Single-layer approach with pronounced drift, rotation, scale breathing,
+ * and color modulation. No multi-layer blending = no geometric artifacts.
+ * Safe because the texture is generated at 8x8 and has no structure.
  */
 
 precision mediump float;
@@ -19,22 +18,25 @@ uniform float u_intensity;
 
 void main() {
     vec2 uv = v_texCoord;
-    float time = u_time * 0.8;
+    float time = u_time;
     float intensity = u_intensity;
+    vec2 center = vec2(0.5);
 
-    // Slow organic drift (Lissajous-like path, never repeats quickly)
+    // === DRIFT: Lissajous-like wandering path ===
+    // Multiple frequencies for organic, non-repeating motion
     vec2 drift = vec2(
-        sin(time * 0.07) * 0.03 + sin(time * 0.03) * 0.02,
-        cos(time * 0.05) * 0.025 + cos(time * 0.02) * 0.015
+        sin(time * 0.13) * 0.12 + sin(time * 0.07 + 1.3) * 0.08,
+        cos(time * 0.11) * 0.10 + cos(time * 0.05 + 2.1) * 0.07
     ) * intensity;
 
-    // Gentle scale breathing around center
-    float scaleBreath = 1.0 + sin(time * 0.09) * 0.02 * intensity;
-    vec2 center = vec2(0.5);
+    // === SCALE: Pronounced breathing (zoom in/out) ===
+    float scaleBreath = 1.0
+        + sin(time * 0.17) * 0.08 * intensity
+        + sin(time * 0.09 + 0.7) * 0.04 * intensity;
     vec2 scaledUV = center + (uv - center) * scaleBreath;
 
-    // Slow rotation
-    float angle = sin(time * 0.04) * 0.015 * intensity;
+    // === ROTATION: Slow but visible swaying ===
+    float angle = (sin(time * 0.08) * 0.06 + sin(time * 0.04 + 1.5) * 0.03) * intensity;
     vec2 centered = scaledUV - center;
     float c = cos(angle);
     float s = sin(angle);
@@ -49,21 +51,27 @@ void main() {
     // Sample texture (MIRRORED_REPEAT handles out-of-range UVs)
     vec3 color = texture(u_texture, finalUV).rgb;
 
+    // === COLOR MODULATION: Warm/cool shifting ===
+    // Slowly shifts hue warmth over time
+    float warmShift = sin(time * 0.06) * 0.08 * intensity;
+    color.r *= 1.0 + warmShift;
+    color.b *= 1.0 - warmShift * 0.6;
+
     // Radial distance from center (0 at center, ~1 at corners)
     float radial = length(uv - center) * 1.414;
 
-    // Subtle pulsing vignette
-    float vignetteStrength = 0.25 + sin(time * 0.12) * 0.05 * intensity;
+    // === VIGNETTE: Pulsing edge darkening ===
+    float vignetteStrength = 0.30 + sin(time * 0.14) * 0.10 * intensity;
     float vignette = 1.0 - radial * vignetteStrength;
     color *= vignette;
 
     // Vertical gradient tint (cool top, warm bottom)
-    vec3 tintTop = vec3(0.96, 0.97, 1.0);
-    vec3 tintBottom = vec3(1.0, 0.97, 0.94);
+    vec3 tintTop = vec3(0.95, 0.97, 1.0);
+    vec3 tintBottom = vec3(1.0, 0.96, 0.93);
     color *= mix(tintBottom, tintTop, uv.y);
 
-    // Gentle brightness breathing
-    float breath = 1.0 + sin(time * 0.15) * 0.06 * intensity;
+    // === BRIGHTNESS BREATHING: Pronounced pulse ===
+    float breath = 1.0 + sin(time * 0.20) * 0.12 * intensity;
     color *= breath;
 
     fragColor = vec4(color, 1.0);