Fix Vulkan texture publication ordering

[cwervo]

Summary

• keep Vulkan texture uploads asynchronous while avoiding sampling unpublished descriptor slots
• drain pending texture descriptor work before canvas and display command recording
• retire freed textures safely by redirecting descriptor slots to debugIm before delayed destruction

Validation

• make
• git diff --check
• deployed to folk@folk-hex.local and folk@folk-cwe.local
• projector capture scan found no debug-magenta frames

[cwervo]

Works on folk-hex, folk-convivial, and on @ppkn's system. Will merge tomorrow unless there are any objections

[osnr]

I still want to read through it more closely and understand the texture pipeline which has gotten pretty weird, but it works on gadget-blue and folk-omar as well so no objection rn