feat(uniform): add 9 volumetric-disk fields to BlackHoleUniforms

Rust and WGSL structs kept in lockstep: 8 f32 tunables + disk_quality
u32 tier. Appended after _pad5; scalar fields pack contiguously so no
explicit padding needed. Defaults mirror BlackHoleParams::default.

assets/shaders/black_hole.wgsl

@@ -39,6 +39,15 @@ struct BlackHoleUniforms {
     bloom_strength: f32,
     exposure: f32,
     _pad5: f32,
+    disk_half_thickness: f32,
+    filament_freq: f32,
+    filament_sharpness: f32,
+    density_freq: f32,
+    density_strength: f32,
+    arm_count: f32,
+    arm_tightness: f32,
+    arm_strength: f32,
+    disk_quality: u32,
 };
 
 @group(#{MATERIAL_BIND_GROUP}) @binding(0) var<uniform> uniforms: BlackHoleUniforms;

src/render/material.rs

@@ -43,6 +43,16 @@ pub struct BlackHoleUniforms {
     pub bloom_strength: f32,
     pub exposure: f32,
     pub _pad5: f32,
+    // Disk volumetric (Phase 3.1)
+    pub disk_half_thickness: f32,
+    pub filament_freq: f32,
+    pub filament_sharpness: f32,
+    pub density_freq: f32,
+    pub density_strength: f32,
+    pub arm_count: f32,
+    pub arm_tightness: f32,
+    pub arm_strength: f32,
+    pub disk_quality: u32,
 }
 
 impl Default for BlackHoleUniforms {
@@ -79,6 +89,15 @@ impl Default for BlackHoleUniforms {
             bloom_strength: 0.8,
             exposure: 1.0,
             _pad5: 0.0,
+            disk_half_thickness: 0.3,
+            filament_freq: 1.0,
+            filament_sharpness: 2.0,
+            density_freq: 0.8,
+            density_strength: 1.0,
+            arm_count: 2.0,
+            arm_tightness: 2.0,
+            arm_strength: 0.5,
+            disk_quality: 3, // High
         }
     }
 }