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/tests/mock_backend.rs

@@ -146,6 +146,11 @@ impl DocApiBackend for MockBackend {
         }
         Ok(self.alloc("AttributeDefinition"))
     }
+    fn add_dimension_angular2ln(&mut self, _spec: &ocs_doc_api::ops::DimensionAngularSpec) -> ApiResult<ObjectId> {
+        let id = self.alloc("Dimension");
+        self.dimension_measurements.insert(id, 90.0); // mock: 90 degrees
+        Ok(id)
+    }
     fn add_table(&mut self, spec: &ocs_doc_api::ops::TableSpec) -> ApiResult<ObjectId> {
         let cols = spec.data.first().map(|r| r.len()).unwrap_or(0);
         if spec.data.is_empty() || cols == 0 || spec.data.iter().any(|r| r.len() != cols) {

crates/ocs_doc_api/tests/spec_wire_consistency.rs

@@ -71,6 +71,7 @@ fn operation_variants() -> Vec<String> {
             tag: String::new(), prompt: String::new(), default_value: String::new(), insertion_point: [0.0; 3], height: 0.0, rotation: 0.0,
         }),
         Operation::CreateTable(ocs_doc_api::ops::TableSpec { insertion_point: [0.0; 3], data: vec![] }),
+        Operation::CreateDimensionAngular2Ln(ocs_doc_api::ops::DimensionAngularSpec { vertex: [0.0; 3], first_point: [0.0; 3], second_point: [0.0; 3], arc_location: [0.0; 3] }),
     ];
     // Derive the variant names by serializing a probe of each and reading the
     // bincode variant index -> name map is not available; instead match by
@@ -165,6 +166,7 @@ const OPERATION_BASELINE: &[&str] = &[
     "CreateDimensionAngular",
     "CreateAttributeDefinition",
     "CreateTable",
+    "CreateDimensionAngular2Ln",
 ];
 
 /// Recorded baseline of the `Query` variant order.