Event wallpaper: party photos on chosen TVs

Rolling out. The server side is in this version of Reelhost. Planning one in Signal arrives in a Signal update.

An event wallpaper shows photos on the TVs you choose, only between a start and an end you set, then those TVs return to their usual screensaver without anyone doing anything.

• Only an admin plans one. Pick a name, the albums, folders or photo libraries to show (up to 50), the TVs (up to 20), the start and end, how long each photo stays and whether to shuffle. It can last 14 days at most and be planned up to a year ahead.
• Times are wall-clock times in a named time zone, such as 18:00 on 24 December in Europe/London, so a clock change doesn't move it. If a time doesn't exist that day, it moves to just after the gap, and the preview tells you.
• Preview first. Before saving you see when it opens and closes, which TVs, and whether another event uses the same TV at the same time (the one that opened last is shown). Saving the same event twice is refused.
• It copies nothing. The photos stay where they are in your Jellyfin libraries. A photo that isn't set to Show on TV and other devices still isn't shown, even when its album is picked.
• Stop it any time. Stopping a running event sends its TVs back at once. Once it's running, only the photos and the pace can change, not the times or the TVs.
• A log. Created, changed, opened, closed and stopped, each with the time. If Reelhost wasn't running when it opened, the log says so.

When you remove Reelhost, saved events and their log are deleted and the TVs show their usual screensaver. Nothing else was made for them.