Resolve platform, hardware model, and friendly device name once via a shared DeviceIdentityService and send them to both backends: Plex gets a real X-Plex-Platform plus X-Plex-Device/X-Plex-Device-Name (shown as Player in dashboards/Tautulli), Jellyfin gets the device name in the MediaBrowser auth header. Transcode and live-TV decision requests keep their pinned platform names, which Plex validates server-side. close #1270