The blog index cards showed placeholder icons even for published posts that
have a hero image. Replace the icon thumb with the post hero (cover-cropped)
for every published card in EN/MK/SI, and add a .blog-thumb--image rule to
mirror the existing featured-card image style. Coming-soon / unpublished cards
keep their icons.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>