perf(pipeline): shared, disk-persisted VkPipelineCache (#69)

vkCreateComputePipelines and vkCreateRayTracingPipelinesKHR were passed
VK_NULL_HANDLE, so the driver couldn't reuse compiled shader binaries
across the pipelines built at startup (4 UI shaders + user/RT pipelines)
or across runs.

Add one process-wide Device::pipelineCache. LoadPipelineCache (called
from Initialize) seeds it from pipeline_cache.bin when the file's
VkPipelineCacheHeaderVersionOne header matches this device's
vendorID / deviceID / pipelineCacheUUID; a stale or foreign blob is
discarded so the driver never rejects it. SavePipelineCache is registered
with std::atexit, serialising the cache at process shutdown without any
explicit teardown hook. Both create sites now pass the cache; a null
handle stays valid, so no create-site null check is needed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

implementations/Crafter.Graphics-ComputeShader.cpp

@@ -82,7 +82,7 @@ void ComputeShader::Load(const std::filesystem::path& spvPath) {
         .layout = VK_NULL_HANDLE,
     };
     Device::CheckVkResult(vkCreateComputePipelines(
-        Device::device, VK_NULL_HANDLE, 1, &info, nullptr, &pipeline));
+        Device::device, Device::pipelineCache, 1, &info, nullptr, &pipeline));
 }
 
 void ComputeShader::Dispatch(VkCommandBuffer cmd,