[good first issue] Add a false-positive example to the recipe guide

[TonyNa-code]

Goal: document one case where GalAid should avoid overconfident diagnosis.

Acceptance checklist:

• Add a realistic false-positive example to the relevant recipe or docs.
• Explain what evidence would make the diagnosis stronger.
• Run npm run check before submitting.

[kaizeenn]

I can take this issue. I’ll send a focused docs PR shortly.