Add a 1200x630 changelog thumbnail as a fourth release artifact, generated
from a shared brand template that mirrors the marketing-site hero / OG image:
warm cream to lavender wash, ink dot-grid, an Instrument Serif headline with a
hand-drawn violet squiggle, a segmented 'CHANGELOG | <version>' sticker badge,
and colored ink-bordered theme chips with solid offset shadows.
- .claude/release-assets/: render-thumbnail.mjs (Playwright renderer),
thumbnail.template.html (brand template), logo.png (TryPost wordmark)
- .claude/commands/release.md: new Step 5b renders the thumbnail; it is
versioned in the artifacts PR alongside the changelog and email
- releases/v1.0.6/thumbnail.png: image for the latest release
805a628f66
