ui-egui keeps only the egui_wgpu paint callback; the shaders, batching and
pipelines are fieldcraft-gpu's view module, so an offscreen picture can draw
with the window's pipelines.
Refs #422
Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo