fix(image): scope sampled-image upload barriers to the real consumer stage (#54)

ImageVulkan hardcoded VK_PIPELINE_STAGE_RAY_TRACING_SHADER_BIT_KHR as the
consuming stage in every layout transition. The UI font atlas is sampled by
a *compute* shader, so the upload barrier's dst scope never covered the real
consumer — a correctness gap, not just lost overlap.

Parameterize the consuming stage per image: store it once at Create
(defaulting to RT, preserving existing RT/example callers) and reuse it in
every Update / UpdateRegion / compressed-Update transition. FontAtlas passes
VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT.

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

implementations/Crafter.Graphics-FontAtlas.cpp

@@ -36,7 +36,10 @@ void FontAtlas::Initialize(GraphicsCommandBuffer cmd) {
         kAtlasSize, kAtlasSize, /*mipLevels*/ 1, cmd,
         VK_FORMAT_R8_UNORM,
         VK_IMAGE_USAGE_TRANSFER_DST_BIT | VK_IMAGE_USAGE_SAMPLED_BIT,
-        VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL
+        VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL,
+        // The atlas is sampled by the UI text *compute* shader, not an RT
+        // pipeline — scope the upload barriers to the real consumer.
+        VK_PIPELINE_STAGE_COMPUTE_SHADER_BIT
     );
     std::memset(image.buffer.value, 0, kAtlasSize * kAtlasSize);
 #else