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 <[email protected]>

README.md

@@ -136,6 +136,10 @@ rebuild with no errors, replayed here at 2× speed.
   (manifold solid B-reps, or trimmed and bounded surfaces sewn into solids) as a base feature
   that later features build on — open a `.step`/`.stp`/`.igs`/`.iges` file, insert one into a
   design, or drop it on the window ([docs/step-import.md](docs/step-import.md)).
+- **Render:** opaque surfaces can use metal fraction, roughness and dielectric IOR in the
+  integrated product viewport and CPU preview PNGs. Existing simple colors remain supported.
+  Fixed direct lighting is a preview; HDRI, refraction and texture maps are not implemented.
+  See [opaque surfaces](docs/render-opaque-pbr.md).
 - **Display meshes** from our own tessellation planner: each face becomes a plan of (u, v)
   points and triangles that shares its edge nodes with its neighbours, so the mesh is watertight.
   Facets follow the chord tolerance, the facet angle and a longest side, with cells at most 2:1
@@ -163,6 +167,7 @@ cargo run --release -p solidcraft -- --sample          # desktop app with a samp
 cargo run --release -p solidcraft-cli -- commands      # the command registry
 cargo run --release -p solidcraft-cli -- run examples/bracket.json --out bracket.step
 cargo run --release -p solidcraft-cli -- snapshot examples/bracket.json --out bracket.png
+cargo run --release -p solidcraft-cli -- render examples/render-studio.json --out product.png
 cargo run --release -p solidcraft -- part.step          # open a STEP file as a new design
 cargo run --release -p solidcraft-cli -- eval part.step # measure an imported STEP file
 cargo xtask ci                                          # fmt, clippy, tests, assets, layers, wasm