feat(python): validated, undoable layer table (doc.layers)

Adds the additive v7 TableOperation request and HostApi::table_operation for
layer create/modify/rename/delete/set-current. Refusals are decided before the
undo step is recorded. Python wrapper, real-IPC audit with DWG/DXF persistence,
IPC round-trip test, Python unit test and docs.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/ocs_plugin_api/src/ipc/client.rs

@@ -482,6 +482,18 @@ impl HostApi for PluginHostApi {
         }
     }
 
+    fn table_operation(&mut self, operation: crate::host::TableOperation) -> Result<Handle, String> {
+        match self.client.request(PluginRequest::TableOperation { operation }) {
+            Ok(PluginResponse::TableResult(result)) => {
+                if result.is_ok() { self.document_cache = OnceCell::new(); }
+                result
+            }
+            Ok(PluginResponse::Error(error)) => Err(error),
+            Ok(other) => Err(format!("unexpected table operation response: {other:?}")),
+            Err(error) => Err(error.to_string()),
+        }
+    }
+
     fn set_selection(&mut self, handles: &[Handle]) -> Result<(), String> {
         match self.client.request(PluginRequest::SetSelection { handles: handles.to_vec() }) {
             Ok(PluginResponse::SelectionResult(result)) => result,