Add monorepo adoption example

[baskduf]

Goal

Add a practical monorepo adoption example that shows how prompt-first harness adoption should handle multiple packages or apps.

Scope

• Add an example report or guide under docs/ or examples/.
• Cover package boundaries, local commands, CI paths, and docs ownership.
• Explain how to avoid creating duplicate harness docs in each package unless needed.
• Include checks run and remaining manual decisions.

Acceptance Criteria

• The example uses docs/templates/adoption-report.md as its shape where practical.
• It explains adopted, adapted, skipped, and deferred harness pieces.
• It preserves target repository architecture as source of truth.
• Docs drift and full local validation pass.

References

• ROADMAP.md
• CONTRIBUTING.md
• docs/adoption-workflow.md