shader: gaussian-speck stars + star_aa toggle + bloom/exposure uniforms

star_color's smoothstep(0.5,0.0,d) with scale=80 produced blocky rectangles
at low render_scale. Replace with a gaussian speck: distance to cell center
with exp(-d²/r²) falloff, producing a round 2-3 pixel anti-aliased disk.
star_aa uniform toggles between the gaussian path (desktop default) and the
old square-cell fast path (web default).

Also adds bloom_threshold/bloom_strength/exposure uniform fields to
BlackHoleUniforms (used by later bloom tasks) with safe defaults.

assets/shaders/black_hole.wgsl

@@ -34,6 +34,10 @@ struct BlackHoleUniforms {
     planet_count: u32,
     steps: u32,
     spin: f32,
+    star_aa: u32,
+    bloom_threshold: f32,
+    bloom_strength: f32,
+    exposure: f32,
     _pad5: f32,
 };
 
@@ -82,17 +86,29 @@ fn hash13(p: vec3<f32>) -> f32 {
 
 fn star_color(dir: vec3<f32>, intensity: f32) -> vec3<f32> {
     let scale = 80.0;
-    let cell = floor(dir * scale);
+    let p = dir * scale;
+    let cell = floor(p);
     let h = hash13(cell);
     let threshold = 0.985;
     if (h > threshold) {
         let b = (h - threshold) / (1.0 - threshold);
         let col = mix(vec3<f32>(0.6, 0.7, 1.0), vec3<f32>(1.0, 0.9, 0.7), b);
-        let f = abs(dir * scale - cell);
+        if (uniforms.star_aa != 0u) {
+            // Gaussian speck: distance to cell center, soft radial falloff.
+            // Produces a round 2-3 pixel anti-aliased disk instead of a square.
+            let center = cell + vec3<f32>(0.5);
+            let dist = length(p - center);
+            let radius = 0.25 + b * 0.4;
+            let falloff = exp(-dist * dist / (radius * radius));
+            return col * b * falloff * 4.0 * intensity;
+        } else {
+            // Original fast path: square-cell smoothstep (blocky but cheap).
+            let f = abs(p - cell);
             let d = max(f.x, max(f.y, f.z));
             let falloff = smoothstep(0.5, 0.0, d);
             return col * b * falloff * 3.0 * intensity;
         }
+    }
     return vec3<f32>(0.0);
 }
 

src/params.rs

@@ -27,6 +27,11 @@ pub struct BlackHoleParams {
     pub planet_count: u32,
     // Kerr (Phase 2; unused in Phase 1)
     pub spin: f32,
+    // Quality (Phase 3: cinematic rendering)
+    pub star_aa: bool,
+    pub bloom_threshold: f32,
+    pub bloom_strength: f32,
+    pub exposure: f32,
 }
 
 impl Default for BlackHoleParams {
@@ -48,6 +53,10 @@ impl Default for BlackHoleParams {
             skybox_intensity: 0.0, // procedural stars only by default
             planet_count: 0,
             spin: 0.0,
+            star_aa: if cfg!(target_arch = "wasm32") { false } else { true },
+            bloom_threshold: 1.0,
+            bloom_strength: 0.8,
+            exposure: 1.0,
         }
     }
 }

src/render/material.rs

@@ -38,6 +38,10 @@ pub struct BlackHoleUniforms {
     pub planet_count: u32,
     pub steps: u32,
     pub spin: f32,       // Phase 2: dimensionless Kerr spin χ = a/M ∈ [0,1].
+    pub star_aa: u32,
+    pub bloom_threshold: f32,
+    pub bloom_strength: f32,
+    pub exposure: f32,
     pub _pad5: f32,
 }
 
@@ -70,6 +74,10 @@ impl Default for BlackHoleUniforms {
             planet_count: 0,
             steps: 300,
             spin: 0.0,
+            star_aa: 1,
+            bloom_threshold: 1.0,
+            bloom_strength: 0.8,
+            exposure: 1.0,
             _pad5: 0.0,
         }
     }

src/render/plugin.rs

@@ -261,5 +261,9 @@ fn mirror_params(
         u.planet_count = params.planet_count;
         u.steps = params.steps;
         u.spin = params.spin;
+        u.star_aa = params.star_aa as u32;
+        u.bloom_threshold = params.bloom_threshold;
+        u.bloom_strength = params.bloom_strength;
+        u.exposure = params.exposure;
     }
 }