Server-runtime focus; supplements doc 13. Headline: 4 concurrent ffmpeg
processes for ONE viewer all transcoding 1080p->2160p with PGS subtitle
burn-in, on uncapped jellyfin container sharing 12-core host with
uncapped Forgejo BlueBuild CI runner (88-99 % CPU). Load avg 15.4 on 12
cores. Throttling+SegmentDeletion still off (doc 13 finding 03 now
non-optional). Top quick-win: enable transcode throttling + segment
deletion + cap RemoteClientBitrateLimit.
