YoutubeVideoBlockData gains an optional `playlistId`. The block now
accepts either a video, a playlist, or both, and either field can be
filled with a raw ID *or* a full youtube.com / youtu.be URL — a
helper extracts the ?v= and ?list= parameters automatically.
Embed routing:
- video only → /embed/<id>?rel=0
- playlist only → /embed/videoseries?list=<plid>&rel=0
- video + playlist → /embed/<id>?list=<plid>&rel=0
- block.params merged via URLSearchParams
Also tweaks ImageGalleryBlock (grid variant): green padding/contain
fit, darker caption gradient, smaller left-aligned label that expands
on hover. Hides post_overview block when no posts and no intro text
(prevents a bare heading on /mediathek).
Peter Meier
354d3f09d3