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/features.md

@@ -1,6 +1,6 @@
 # Features
 
-SolidCraft's commands by area, generated by `cargo xtask features` from the command registry (`solidcraft-cli commands`). **354 commands.** Planned (registered, not built yet): 6. Every command runs the same way from the toolbar, a script, `solidcraft-cli exec <id> '<json>'`, the control channel and MCP; parameters are in the [command reference](book/src/reference/commands.md) (`cargo xtask book`). Status and plans: [ROADMAP](../ROADMAP.md).
+SolidCraft's commands by area, generated by `cargo xtask features` from the command registry (`solidcraft-cli commands`). **363 commands.** Planned (registered, not built yet): 6. Every command runs the same way from the toolbar, a script, `solidcraft-cli exec <id> '<json>'`, the control channel and MCP; parameters are in the [command reference](book/src/reference/commands.md) (`cargo xtask book`). Status and plans: [ROADMAP](../ROADMAP.md).
 
 ## Sketch (99)
 
@@ -517,13 +517,20 @@ SolidCraft's commands by area, generated by `cargo xtask features` from the comm
 | Insert Part | `parts.insert` | – |
 | Change Part Size | `parts.resize` | – |
 
-## `render.*` (3)
+## `render.*` (10)
 
 | Command | Id | Toolbar |
 |---|---|---|
+| Check Render Request | `render.preflight` | – |
+| Render Image | `render.start` | RENDER › IMAGE |
+| Render Progress | `render.status` | – |
+| Cancel Render | `render.cancel` | – |
+| Export Render Image | `render.export` | – |
 | Render Backends | `render.backends` | – |
 | Render Settings | `render.settings.get` | – |
 | Save Render Settings | `render.settings.set` | – |
+| Inspect Render Scene | `render.scene` | RENDER › SCENE |
+| Apply Render Camera | `render.settings.apply` | – |
 
 ## `select.*` (2)