feat(vulkan-rt): BLAS build options — fast-build/fast-trace + in-place refit (#36)

Mesh::Build / BuildProcedural now take an RTBuildOptions { preference,
allowUpdate }. `preference` maps to PREFER_FAST_TRACE (default) or
PREFER_FAST_BUILD; `allowUpdate` sets ALLOW_UPDATE so the BLAS can be
refit later.

Adds Mesh::Refit / RefitProcedural: when the original build opted into
allowUpdate and the topology is unchanged, they record an in-place
UPDATE-mode build (src == dst) — much cheaper than a rebuild, and the
AS handle + blasAddr are preserved so TLAS instances stay valid. They
fall back to a full rebuild otherwise. The shared build tail also now
destroys a stale AS handle on re-Build (previously leaked) and guards
the in-place update with an AS read→write barrier.

The portable RTBuildPreference/RTBuildOptions types and Refit methods
also exist on the WebGPU backend for API symmetry; the software BVH has
no hardware AS, so the preference is a no-op and a "refit" rebuilds the
BVH (re-registering the handle).

Also adds Device::validationErrorCount, bumped by the debug-messenger
callback on ERROR-severity messages, so tests can assert a Vulkan
operation produced no validation errors.

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

interfaces/Crafter.Graphics-Device.cppm

@@ -184,6 +184,13 @@ export namespace Crafter {
         // path and RTPass pushes the active TLAS address as push data. Delete
         // this flag and everything keyed on it once a fixed driver ships.
         inline static bool workaroundDescriptorHeapAS = false;
+
+        // Count of ERROR-severity validation messages seen by the debug
+        // messenger callback since instance creation. The callback only
+        // prints (it never aborts), so tests that want to fail on a
+        // validation error — e.g. a malformed acceleration-structure build —
+        // assert this stays zero across the operation under test.
+        inline static std::uint32_t validationErrorCount = 0;
         // The byte offset of the TLAS-address member inside a patched shader's
         // push-constant block is tracked per-shader (VulkanShader::tlasPushOffset),
         // not here: a single global is clobbered by whichever shader was patched