feat(renderer): add PBR material, sphere generator, Cook-Torrance shader, and PBR pipeline

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/voltex_renderer/src/material.rs

@@ -0,0 +1,51 @@
+use bytemuck::{Pod, Zeroable};
+
+#[repr(C)]
+#[derive(Copy, Clone, Debug, Pod, Zeroable)]
+pub struct MaterialUniform {
+    pub base_color: [f32; 4],
+    pub metallic: f32,
+    pub roughness: f32,
+    pub ao: f32,
+    pub _padding: f32,
+}
+
+impl MaterialUniform {
+    pub fn new() -> Self {
+        Self {
+            base_color: [1.0, 1.0, 1.0, 1.0],
+            metallic: 0.0,
+            roughness: 0.5,
+            ao: 1.0,
+            _padding: 0.0,
+        }
+    }
+
+    pub fn with_params(base_color: [f32; 4], metallic: f32, roughness: f32) -> Self {
+        Self {
+            base_color,
+            metallic,
+            roughness,
+            ao: 1.0,
+            _padding: 0.0,
+        }
+    }
+
+    pub fn bind_group_layout(device: &wgpu::Device) -> wgpu::BindGroupLayout {
+        device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+            label: Some("Material Bind Group Layout"),
+            entries: &[wgpu::BindGroupLayoutEntry {
+                binding: 0,
+                visibility: wgpu::ShaderStages::FRAGMENT,
+                ty: wgpu::BindingType::Buffer {
+                    ty: wgpu::BufferBindingType::Uniform,
+                    has_dynamic_offset: true,
+                    min_binding_size: wgpu::BufferSize::new(
+                        std::mem::size_of::<MaterialUniform>() as u64,
+                    ),
+                },
+                count: None,
+            }],
+        })
+    }
+}