Preserve operator layout when reopening saved workflows

Users have reported that when reopening a saved workflow, the layout is not preserved. Specifically, all operators appear clustered in one location instead of maintaining their previous positions.

Suggestion from users:
The canvas should retain and restore the operator positions from the last saved state when reopening the workflow.

No file, test, or entry point is named in the issue. Start by tracing the workflow save and reopen path together with the canvas layout state, reproduce the problem using operators at distinct positions, and verify that reopening restores those positions.

Written by the indexing model from the issue text.