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/lib.rs

@@ -7,8 +7,11 @@
 mod backend;
 mod camera;
 mod curve_display;
+pub mod job;
 pub mod lighting;
+mod product;
 mod raster;
+pub mod studio;
 pub mod surface;
 pub mod texture_input;
 
@@ -19,4 +22,5 @@ pub use backend::{
 };
 pub use camera::{Camera, CameraAnim, Mat4, Quat, StandardView, UpAxis, ease_in_out};
 pub use curve_display::{PixelCurveView, SampledPath, SamplingBudget, SamplingQuality, sample_segment, sample_segment_unclipped};
+pub use product::{FaceAppearance, ProductMesh, ProductScene};
 pub use raster::{Canvas, Rgb, SECTION_CAP, Scene, SceneLine, SceneMesh, png, render, render_png, render_transparent};