ocs_doc_api: Phase 2b-c (linear Dimension) — Phase 2 complete

- CreateDimensionLinear(DimensionSpec) op + GetDimensionMeasurement query (append-only).
- backend add_dimension_linear (Dimension::Linear via DimensionLinear::new) +
  dimension_measurement (linear/radius/diameter distance).
- Dimension bounds from measured + definition points; Dimension handle + measurement().
- spec Dimension family; api_reference + binding_schema regenerated; mocks + baseline.
- Test phase2c_dimension_linear_create_measurement_bounds -> 607 host lib + 8 crate
  + 3 consistency green. Phase 2 (full 2D + annotations) is now complete.

crates/ocs_doc_api/src/query.rs

@@ -47,6 +47,8 @@ pub enum QueryResult {
     TextContent(String),
     /// A hatch's boundary loops (outer + islands), each a closed polyline.
     HatchBoundary(Vec<Vec<[f64; 2]>>),
+    /// A dimension's measured value (distance for linear/radius, degrees for angular).
+    DimensionMeasurement(f64),
 }
 
 /// Convenience: the query name for diagnostics.
@@ -62,6 +64,7 @@ impl crate::gen::Query {
             GetGeometryRevision => "GetGeometryRevision",
             GetTextContent { .. } => "GetTextContent",
             GetHatchBoundary { .. } => "GetHatchBoundary",
+            GetDimensionMeasurement { .. } => "GetDimensionMeasurement",
         }
     }
 }