Zci514/dsh-nightwatch

Keep this session working until a wall-clock deadline: one button in the composer picks 22:30, +90m, or tomorrow 07:00, and after every finished turn the plugin posts one continuation message so the session keeps working; nothing is posted once the deadline passes. Stops early on a round cap (400), three consecutive failed turns, or four consecutive rounds that called no tool; a manual stop button is always there. The last part of the watch switches to wrap-up wording, sized to at most half the remaining time so a short watch is not entirely wrap-up. Armings persist to $DSH_HOME/nightwatch.json via an atomic write and are re-adopted after a restart. No slash command is registered by default (enableCommand turns one on); the continuation message carries source.kind cordis-host-runner, not user.