add case studies and proof points

[github-actions]

Summary

Add credible, concrete examples that show why Workbench improves clarity and
throughput compared to ad-hoc workflows.

Acceptance criteria

• At least 2 “before/after” snapshots showing how work is captured with and
  without Workbench.
• One end-to-end narrative that traces a work item from creation to PR.
• Documented outcomes or metrics (even qualitative) that reinforce the value.