Add post video upload (#22)

Questions and replies can attach one MP4 or WebM (25 MB) alongside up to four images. Videos are stored as-is and omitted from Discord embeds.

Reviewed-on: #22
Co-authored-by: codegirl-007 <s.raide@gmail.com>

internal/web/events.go

@@ -55,6 +55,9 @@ func (s *Server) postEvent(post, root *store.Post, author *store.User) events.Po
 	if n := len(post.Images); n > 0 {
 		ev.Images = make([]events.Image, 0, n)
 		for _, img := range post.Images {
+			if img.Kind == store.MediaKindVideo {
+				continue
+			}
 			ev.Images = append(ev.Images, events.Image{
 				URL:         img.PublicURL,
 				Description: img.Description,