ocs_doc_api: Phase 2c-iii — 2-line angular dimension (all dimension sub-types done)

- CreateDimensionAngular2Ln(DimensionAngularSpec) op (append-only).
- backend add_dimension_angular2ln (DimensionAngular2Ln::new computes angle).
- facade create_dimension_angular2ln; spec constructor; api_reference + binding_schema
  regenerated; mocks + baseline.
- IMPLEMENTATION.md: fix stale Status line (all 5 phases complete, current test
  counts); mark all dimension sub-types done.
- Test phase2ciii_dimension_angular2ln (90-degree 2-line angle) -> 616 host lib +
  3 consistency green.

crates/ocs_doc_api/src/ops.rs

@@ -233,6 +233,7 @@ impl crate::gen::Operation {
             CreateDimensionAngular(_) => "CreateDimensionAngular",
             CreateAttributeDefinition(_) => "CreateAttributeDefinition",
             CreateTable(_) => "CreateTable",
+            CreateDimensionAngular2Ln(_) => "CreateDimensionAngular2Ln",
         }
     }
 }