Photo notes and published galleries

Arrange larger photo stories in Letter.md and publish them as responsive, browsable galleries.

Photo notes can now move from a working collection to a public story without rebuilding the layout elsewhere.

What changed

Arrange and reorder photos directly in an image document.
Build photo grids with more than nine images.
Publish photo notes with a responsive grid and focused image viewer.
Keep stable image URLs across updates.
Preserve titles, descriptions, and Markdown fallbacks alongside the visual layout.

The published page is a snapshot, so later edits stay private until you update the publication.