ocs_doc_api: Phase 4 set_view + viewport-view query

- SetViewportView op + GetViewportView query (append-only).
- backend set_viewport_view (update Viewport.view_target/view_height) + viewport_view.
- facade Entity::set_view/viewport_view (Viewport returns Entity).
- spec Viewport methods; api_reference + binding_schema regenerated; mocks + baseline.
- Test phase4_set_view_and_view_query -> 609 host lib + 3 consistency green.
- Phase 4 complete.

crates/ocs_doc_api/src/gen/ops_gen.rs

@@ -42,4 +42,6 @@ pub enum Operation {
     CreateDimensionLinear(DimensionSpec),
     // attributes
     SetAttribute { id: ObjectId, tag: String, value: String },
+    // viewport view
+    SetViewportView { id: ObjectId, view_target: [f64; 3], view_height: f64 },
 }