Adds CompositeMaterial + composite.wgsl: combines the HDR scene with the bloom pyramid output, applies ACES (Narkowicz) tone mapping, and writes LDR to the window. Removes UpscaleMaterial + upscale.wgsl. mirror_params now updates composite (bloom_strength, exposure) and brightpass (threshold) uniforms each frame. resize_offscreen rebuilds the full bloom pyramid targets on window resize.