Render R2: persist named render setups without re-evaluating geometry (#667)

render.settings.set saves validated named render setups (camera, output size, exposure, environment) as one undo step, and render.settings.get reads them back without applying a camera. When validated render settings are the only change, the engine keeps the evaluated model instead of rebuilding it. Setups are saved under design format 21; format-20 designs read as having none. Fixes #658; refs #620.

Contributed by @0xlillith.

Co-authored-by: lillith <35337584+0xlillith@users.noreply.github.com>

Cargo.lock

@@ -3488,6 +3488,7 @@ dependencies = [
  "sha2",
  "solidcraft-geom",
  "solidcraft-kernel",
+ "solidcraft-render",
  "solidcraft-sketch",
  "thiserror 2.0.21",
  "web-time",