The OG generation in the eleventy.before hook consumed too much memory
alongside Eleventy's data cascade, causing the Eleventy process to be
OOM-killed on Cloudron. Fix by running OG generation in a separate
child process with its own 768MB heap limit. Also write the manifest
incrementally (every 10 images) to preserve progress if interrupted.
Uses Satori + @resvg/resvg-js to create branded 1200x630 social
preview cards at build time. Cards show post title, type badge,
date, and site name on a dark background with blue accent.
Generated images are cached in .cache/og/ (persistent on Cloudron)
and passthrough-copied to the output. Posts with photos continue
using their own images. Untitled posts (notes) use body text.