feat(renderer): add HDR target, Bloom resources, and ACES tonemap

- Add hdr.rs with HdrTarget (Rgba16Float render target) and HDR_FORMAT constant
- Add bloom.rs with BloomResources (5-level mip chain), BloomUniform, and mip_sizes()
- Add tonemap.rs with TonemapUniform and CPU-side aces_tonemap() for testing
- Export all new types from lib.rs
- 33 tests passing (26 existing + 3 bloom + 4 tonemap)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

crates/voltex_renderer/src/hdr.rs

@@ -0,0 +1,43 @@
+/// Texture format used for HDR render targets.
+pub const HDR_FORMAT: wgpu::TextureFormat = wgpu::TextureFormat::Rgba16Float;
+
+/// An HDR render target (Rgba16Float) used as the output of the lighting pass.
+pub struct HdrTarget {
+    pub view: wgpu::TextureView,
+    pub width: u32,
+    pub height: u32,
+}
+
+impl HdrTarget {
+    pub fn new(device: &wgpu::Device, width: u32, height: u32) -> Self {
+        let view = create_hdr_view(device, width, height);
+        Self { view, width, height }
+    }
+
+    /// Recreate the HDR texture when the window is resized.
+    pub fn resize(&mut self, device: &wgpu::Device, width: u32, height: u32) {
+        self.view = create_hdr_view(device, width, height);
+        self.width = width;
+        self.height = height;
+    }
+}
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+fn create_hdr_view(device: &wgpu::Device, width: u32, height: u32) -> wgpu::TextureView {
+    let texture = device.create_texture(&wgpu::TextureDescriptor {
+        label: Some("HDR Target Texture"),
+        size: wgpu::Extent3d {
+            width,
+            height,
+            depth_or_array_layers: 1,
+        },
+        mip_level_count: 1,
+        sample_count: 1,
+        dimension: wgpu::TextureDimension::D2,
+        format: HDR_FORMAT,
+        usage: wgpu::TextureUsages::RENDER_ATTACHMENT | wgpu::TextureUsages::TEXTURE_BINDING,
+        view_formats: &[],
+    });
+    texture.create_view(&wgpu::TextureViewDescriptor::default())
+}