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]>

docs/mcp.md

@@ -5,6 +5,11 @@ SolidCraft speaks the [Model Context Protocol](https://modelcontextprotocol.io)
 An agent models exactly like a person does: every tool runs engine commands, the same ones the
 toolbar, palette, scripts and control channel use, and never opens a dialog.
 
+Persistent headless and bridged sessions expose asynchronous product images through the
+ordinary `execute` tool: `render.preflight`, `render.start`, `render.status`,
+`render.cancel` and `render.export`. Keep the complete returned job ID; image bytes remain
+in the session until explicit PNG export. See [render jobs](render-jobs.md).
+
 ## Start it
 
 ```sh