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>

examples/render-opaque-studio.json

@@ -0,0 +1,15 @@
+{
+  "commands": [
+    {"command":"file.new","params":{"name":"Original opaque surface study"}},
+    {"command":"solid.sphere","params":{"body_name":"Nonmetal smooth","radius":10,"center":[-36,0,12]}},
+    {"command":"solid.sphere","params":{"body_name":"Nonmetal rough","radius":10,"center":[-12,0,12]}},
+    {"command":"solid.sphere","params":{"body_name":"Metal smooth","radius":10,"center":[12,0,12]}},
+    {"command":"solid.sphere","params":{"body_name":"Metal rough","radius":10,"center":[36,0,12]}},
+    {"command":"appearance.assign","params":{"bodies":["Nonmetal smooth"],"appearance":"Original nonmetal smooth","color":"#b47846","pbr":{"metallic":0,"roughness":0.2,"dielectric_ior":1.5}}},
+    {"command":"appearance.assign","params":{"bodies":["Nonmetal rough"],"appearance":"Original nonmetal rough","color":"#b47846","pbr":{"metallic":0,"roughness":0.65,"dielectric_ior":1.5}}},
+    {"command":"appearance.assign","params":{"bodies":["Metal smooth"],"appearance":"Original metal smooth","color":"#b47846","pbr":{"metallic":1,"roughness":0.2,"dielectric_ior":1.5}}},
+    {"command":"appearance.assign","params":{"bodies":["Metal rough"],"appearance":"Original metal rough","color":"#b47846","pbr":{"metallic":1,"roughness":0.65,"dielectric_ior":1.5}}},
+    {"command":"solid.box","params":{"body_name":"Study base","corner":[-49,-14,0],"length":98,"width":28,"height":2}},
+    {"command":"appearance.assign","params":{"bodies":["Study base"],"color":"#ccd0d4"}}
+  ]
+}