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/examples/common/mod.rs

@@ -206,6 +206,13 @@ impl DocApiBackend for MockBackend {
         }
         Ok(self.alloc("AttributeDefinition"))
     }
+    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) {
+            return Err(ApiError::validation("CreateTable", "table needs a non-empty rectangular grid"));
+        }
+        Ok(self.alloc("Table"))
+    }
     fn set_attribute(&mut self, id: ObjectId, tag: &str, value: &str) -> ApiResult<()> {
         if !self.entity_exists(id) {
             return Err(ApiError::UnknownId(id));