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/gen/query_gen.rs

@@ -23,4 +23,6 @@ pub enum Query {
     GetTextContent { id: ObjectId },
     /// The boundary loops of a Hatch (outer + islands) as polylines.
     GetHatchBoundary { id: ObjectId },
+    /// The measured value of a Dimension (distance or angle).
+    GetDimensionMeasurement { id: ObjectId },
 }