Upload Element Previews

1. Identify the Element slug. Ask if it is ambiguous.
2. Choose the source:
   • Use render for fresh files in .element-previews.
   • Use submission for committed files in static/elements.
3. Upload the previews:

cd packages/docs
bun run upload-element-preview \
  --element=<category>/<slug> \
  --source=<render|submission>

Each upload uses a new random URL postfix, including when the Element already has hosted previews. This keeps previews from concurrent branches independent.

4. Replace image, posterUrl, and videoUrl with the newly printed remotion.media URLs.
5. If using submission, delete the local review assets. If using render, leave .element-previews uncommitted.
6. Commit and push when the work belongs on a branch.