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/ui-egui/src/control.rs

@@ -185,10 +185,22 @@ pub fn handle(app: &mut SolveApp, ctx: &egui::Context, req: &ControlRequest) ->
 }
 
 fn dispatch(app: &mut SolveApp, ctx: &egui::Context, method: &str, p: &Value) -> Outcome {
+    crate::render_workspace::sync_backend(app);
     let s = |k: &str| p.get(k).and_then(Value::as_str);
     let f = |k: &str| p.get(k).and_then(Value::as_f64).filter(|x| x.is_finite());
     let b = |k: &str| p.get(k).and_then(Value::as_bool).unwrap_or(false);
     match method {
+        "ui.workspace" => {
+            if let Some(workspace) = s("workspace") {
+                if !matches!(workspace, "design" | "render") {
+                    return err("workspace must be design or render");
+                }
+                if let Err(e) = crate::render_workspace::enter(app, workspace == "render") {
+                    return err(e);
+                }
+            }
+            ok(json!({"workspace":if crate::render_workspace::active(app) {"render"} else {"design"}}))
+        }
         "engine.execute" | "command" => {
             let Some(id) = s("command").or(s("id")) else { return err("missing `command`") };
             wrap(execute(app, id, p.get("params").cloned().filter(|v| !v.is_null()).unwrap_or(json!({}))))
@@ -230,6 +242,7 @@ fn dispatch(app: &mut SolveApp, ctx: &egui::Context, method: &str, p: &Value) ->
             "frame_ms": app.frame_ms,
             "file_busy": app.file_load.busy(),
             "file_picker_busy": app.file_picker_busy(),
+            "file_dialog_open": app.file_picker_busy(),
             "build_ms": app.viewport.build_ms,
             "preview": {"active": app.preview.active, "busy": app.preview.busy, "error": app.preview.error, "ms": app.preview.ms, "replaced": app.preview.replaced},
             "home": app.home.open,
@@ -283,6 +296,11 @@ fn dispatch(app: &mut SolveApp, ctx: &egui::Context, method: &str, p: &Value) ->
             }
             match (serde_json::from_value::<crate::UiState>(cur), serde_json::from_value::<solidcraft_engine::Visibility>(vis)) {
                 (Ok(u), Ok(v)) => {
+                    if (u.tab == "RENDER") != crate::render_workspace::active(app)
+                        && let Err(e) = crate::render_workspace::enter(app, u.tab == "RENDER")
+                    {
+                        return err(e);
+                    }
                     app.ui = u;
                     app.session.visibility = v;
                     ok(serde_json::to_value(&app.ui).unwrap_or_default())