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>
