ocs_doc_api: Phase 2c-ii — dimension sub-types (radius/diameter/angular)

- CreateDimensionRadius/CreateDimensionDiameter (DimensionRadialSpec) +
  CreateDimensionAngular (DimensionAngularSpec) ops (append-only).
- backend add_dimension_radius/diameter (DimensionRadius/DimensionDiameter::new)
  + add_dimension_angular (DimensionAngular3Pt::new computes angle);
  dimension_measurement returns degrees for angular sub-types.
- facade create_dimension_radius/diameter/angular; spec constructors; api_reference
  + binding_schema regenerated; mocks + baseline.
- Test phase2cii_dimension_radius_diameter_angular -> 613 host lib + 3 consistency green.

crates/ocs_doc_api/src/backend.rs

@@ -63,6 +63,15 @@ pub trait DocApiBackend {
     /// Add a linear `DIMENSION`; returns the fresh `ObjectId`.
     fn add_dimension_linear(&mut self, spec: &crate::ops::DimensionSpec) -> ApiResult<ObjectId>;
 
+    /// Add a radial `DIMENSION`; returns the fresh `ObjectId`.
+    fn add_dimension_radius(&mut self, spec: &crate::ops::DimensionRadialSpec) -> ApiResult<ObjectId>;
+
+    /// Add a diameter `DIMENSION`; returns the fresh `ObjectId`.
+    fn add_dimension_diameter(&mut self, spec: &crate::ops::DimensionRadialSpec) -> ApiResult<ObjectId>;
+
+    /// Add a 3-point angular `DIMENSION`; returns the fresh `ObjectId`.
+    fn add_dimension_angular(&mut self, spec: &crate::ops::DimensionAngularSpec) -> ApiResult<ObjectId>;
+
     /// A dimension's measured value (distance for linear/radius, degrees for angular).
     fn dimension_measurement(&self, id: ObjectId) -> ApiResult<f64>;