Workflow versioning: track, compare, and roll back changes

**What the feature is (as Title)**

Workflow versioning: track, compare, and roll back changes

**Value proposition**

Automation that acts on production systems demands change control. Every change to a workflow is now tracked automatically: users can view the full change history, compare any two versions to see exactly what changed, and roll back to a known-good version in one click. Teams can iterate on production automations without fear of losing a working state, with an auditable record of who changed what and when.

**Expected outcome**

- Automatic version history for every workflow, captured on save regardless of whether the change came from the UI or the API
- Side-by-side diff between any two versions
- One-click rollback to any prior version
- An auditable change record that supports compliance and change-management requirements

**Optional: Key user stories / use cases**

- Diagnosing why a workflow's behavior changed by reviewing its change timeline
- Restoring a working version after a bad edit
- Evidencing change control for regulated environments