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/backend.rs

@@ -75,6 +75,12 @@ pub trait DocApiBackend {
     /// The entities inside a block definition (read-only traversal), as views.
     fn block_entities(&self, block_name: &str) -> ApiResult<Vec<EntityView>>;
 
+    /// Set a viewport's view target + zoom height in place. Viewport-only.
+    fn set_viewport_view(&mut self, id: ObjectId, view_target: [f64; 3], view_height: f64) -> ApiResult<()>;
+
+    /// A viewport's view (target WCS + zoom height). Viewport-only.
+    fn viewport_view(&self, id: ObjectId) -> ApiResult<([f64; 3], f64)>;
+
     /// Can `id` be modified in place right now (exists, is the expected family,
     /// not on a locked layer)? Read-only pre-check used before mutations.
     /// Default: existence + not-locked (backends narrow the family check).