ChanServ: add SET AUTOOP

SET AUTOOP {ON|OFF} controls whether access members are auto-opped/voiced
on join (on by default). Stored inverted as a settings flag so the
default stays on, and gated in the join handler.

api/src/lib.rs

@@ -756,6 +756,8 @@ pub enum ChanSetting {
     TopicLock,
     // Kick users without channel access when they join.
     Restricted,
+    // Auto-op/voice access members on join (on by default).
+    AutoOp,
     // BotServ: show members' personal greets on join.
     BotGreet,
     // BotServ: forbid the founder from (un)assigning a bot (admin override only).