One sky for everyone, shorter and darker nights

From the first alpha playtest (items 7, 8, 10): every player saw their own time of day, the night came at 19:00 and lasted ten game hours, and it was a bright saturated blue.

• The server owns the world clock: the hour is a pure function of the server's game time with a 115-minute world day (uo_proto::clock::world_hour, DAY_MS); Welcome carries day_ms and time_scale, the client keeps a WorldClock synced by its pings.
• Dusk at 21:00, full night 21:48 to 4:00, the sun's arc 5:24 to 20:48.
• Night darker and its moonlit blue less saturated.