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/query_gen.rs

@@ -30,4 +30,6 @@ pub enum Query {
     GetAttributes { id: ObjectId },
     /// The entity ids + kinds inside a block definition (read-only traversal).
     GetBlockEntities { block_name: String },
+    /// A viewport's view (target + zoom height).
+    GetViewportView { id: ObjectId },
 }