[feature] Workflow diffs

**As a** Workflow developer

**I want to** see workflow diffs in the workflow history, when upgrading projects in project deployments, and when updating workflows from a Git repository

**So that** I can see all changes between workflow versions in all the above situations

Technical Details
TODO

Acceptance Criteria
TODO

Definition of Done
TODO

Start by mapping the existing workflow-history, project-deployment upgrade, and Git repository update flows. Confirm how workflow versions are represented and where each flow exposes changes, then define acceptance criteria for showing diffs in all three contexts. Done means users can see all changes between workflow versions in each listed situation.

Written by the indexing model from the issue text.