Compatibility: add one versioned viewer report

[OthmaneBlial]

Goal

Run one canonical synthetic fixture in one currently unverified or newer PowerPoint-compatible viewer and publish a bounded result.

Allowed files

• docs/VIEWER_MATRIX.md
• docs/EXPORT_COMPATIBILITY.md only when a limitation is confirmed
• docs/assets/viewer-reports/ for sanitized screenshots

Fixture

Use docs/fixtures/product-brief.pptx or one checked-in gallery deck. Do not upload private decks. Google Slides testing requires the contributor to authorize that upload explicitly.

Acceptance criteria

• Record viewer name/version, OS, exact fixture, commit, and date.
• Check page count, selectable/editable text, shape bounds, notes, charts or tables when present, and any reflow.
• Attach a screenshot with private notifications and unrelated windows excluded.
• Report PASS, PARTIAL, or FAIL with concrete limitations.
• Do not generalize beyond the tested viewer/version.

Maintainer availability

Claim the viewer here before testing. A maintainer will confirm the fixture and expected checks.

Out of scope

Private files, broad parity claims, or screenshots containing unrelated desktop content.