Render: integrated workspace, preview image jobs and opaque PBR (#1046)

Lands the Render workspace (R3), bounded preview-image jobs with cancellation and atomic PNG export (R4a), and opaque PBR looks as one change.

- Render workspace: an overlay-free product preview on the installed GPU device. Returning to Design restores its camera. render.scene and render.settings.apply are added.
- Image jobs: render.preflight/start/status/cancel/export run bounded CPU preview jobs. Export captures the job, overwrite choice and document, and checks the caller's file scope before writing.
- Opaque PBR: looks can carry metal fraction, roughness and dielectric IOR. The product viewport and preview PNG use them; geometry and mass are unchanged. The v1 catalog export refuses PBR rather than dropping it.
- Render setups and PBR looks are saved under design format 21. Labels are in en/de/ja/ko/zh/ru.

Supersedes #706 and #800. Refs #620, #673, #756, #1004.

Contributed by @0xlillith.

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

crates/ui-egui/src/menu_tests.rs

@@ -660,11 +660,12 @@ fn toolbar_pins_removes_reorders_and_keeps_its_layout() {
 }
 
 #[test]
-fn the_workspace_menu_lists_design_and_greys_the_rest() {
+fn the_workspace_menu_lists_design_and_render_and_greys_future_workspaces() {
     let app = sample_app();
     let items = context_menu::items(&app, &Target::Workspace);
     assert!(find(&items, "Design").enabled);
-    assert!(!find(&items, "Render").enabled && find(&items, "Render").shortcut == "coming later");
+    assert!(find(&items, "Render").enabled);
+    assert!(!find(&items, "Animation").enabled);
     assert!(!items.iter().any(|i| i.label.contains("Generative")));
 }