docs: add quickstart screenshots or terminal transcript

[devswha]

Goal

Add a compact install-and-run transcript or screenshot-style terminal block to the README or docs.

Why

New visitors should be able to understand the first successful run in under a minute.

Suggested scope

• Show install command.
• Show /patina --lang en or standalone patina --lang en input.txt.
• Show a short output excerpt from audit, diff, or score mode.

Acceptance criteria

• The example does not require exposing API keys or local secrets.
• The transcript is short enough to scan.
• README stays focused; put longer output in docs if needed.