ocs_doc_api: Phase 5-ii — typed Table create

- CreateTable(TableSpec{insertion_point, data[row][col]}) op (append-only).
- backend add_table via Table::new(insertion_point, rows, cols) + set_cell_text
  (Table::default() pre-creates 3x3, so use Table::new for exact dims).
- executor validates non-empty rectangular grid; facade create_table.
- spec Table constructor; api_reference + binding_schema regenerated; mocks + baseline.
- Test phase5ii_create_table_from_grid (3x2 grid, non-rectangular rejected)
  -> 615 host lib + 3 consistency green. Phase 5 complete.

crates/ocs_doc_api/src/backend.rs

@@ -75,6 +75,9 @@ pub trait DocApiBackend {
     /// Add an `ATTDEF` (in-block attribute definition); returns the fresh `ObjectId`.
     fn add_attribute_definition(&mut self, spec: &crate::ops::AttributeDefinitionSpec) -> ApiResult<ObjectId>;
 
+    /// Add a `TABLE` (rows × columns grid); returns the fresh `ObjectId`.
+    fn add_table(&mut self, spec: &crate::ops::TableSpec) -> ApiResult<ObjectId>;
+
     /// A dimension's measured value (distance for linear/radius, degrees for angular).
     fn dimension_measurement(&self, id: ObjectId) -> ApiResult<f64>;