[Help wanted] Add one rendered-preview review fixture

[ch040602]

Goal:
Add or improve one rendered-preview review fixture so mdpr-skill can turn visual evidence into actionable review notes.

Scope:

• Use a small committed Markdown source, manifest summary, rendered PNG, contact sheet, or report fixture.
• The review note should point to evidence paths and describe the concern at the MDPR rule/config level.
• Keep the artifact compact and reproducible.

Evidence:

• PNG/PPTX/manifest/report path when output changes.
• Focused validation command, such as npm run test:cli-main, npm run test:schema-sync, or a relevant unittest.

Boundary:
The fixture may describe clipping, readability, coherence, contrast, or connector concerns, but MDPR validation remains the pass/fail authority.