ocs_doc_api: Phase 3 (block references)

- Operation::CreateInsert(InsertSpec) appended to the wire enum (append-only).
- backend add_insert validates the BlockRecord exists (unknown block -> Validation,
  no mutation); host inserts acadrust::entities::Insert with scale+rotation.
- Insert transform moves insert_point (transform_entity_geometry) +
  ensure_transformable includes Insert.
- facade EntityCollection::create_insert; spec Insert family; api_reference +
  binding_schema regenerated; mocks updated.
- Test phase3_create_insert_and_transform -> 599 host lib green.
- IMPLEMENTATION.md: Phase 3 done (attributes/traversal remaining).

crates/ocs_doc_api/src/gen/binding_schema.json

@@ -187,6 +187,13 @@
       "handle": "XLine",
       "methods": [],
       "name": "XLine"
+    },
+    {
+      "acadrust_variant": "Insert",
+      "collection": "entities",
+      "handle": "Entity",
+      "methods": [],
+      "name": "Insert"
     }
   ],
   "layouts": {