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/render/src/raster.rs

@@ -79,7 +79,7 @@ impl Canvas {
     }
 }
 
-fn shade(n: Vec3, view_dir: Vec3, base: [f64; 3]) -> [f64; 3] {
+pub(crate) fn shade(n: Vec3, view_dir: Vec3, base: [f64; 3]) -> [f64; 3] {
     let n = if n.dot(view_dir) < 0.0 { -n } else { n };
     let key = (view_dir * 0.8 + Vec3::new(-0.3, 0.2, 0.6)).normalized().unwrap_or(view_dir);
     let diff = n.dot(key).max(0.0);