chanserv: op, deop, voice, devoice, kick, ban, unban

Adds channel moderation commands sourced from the ChanServ pseudoclient.
Tracks connected users' nicks and hosts so targets can be resolved by
nick and banned by *!*@host. All commands require operator access.

modules/chanserv/ban.rs

@@ -0,0 +1,22 @@
+use crate::engine::db::Db;
+use crate::engine::service::{Sender, ServiceCtx};
+use crate::engine::state::Network;
+
+// BAN <#channel> <nick> [reason]: ban *!*@host and kick the user.
+pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, net: &Network, db: &Db) {
+    let (Some(&chan), Some(&nick)) = (args.get(1), args.get(2)) else {
+        ctx.notice(me, from.uid, "Syntax: BAN <#channel> <nick> [reason]");
+        return;
+    };
+    if !super::require_op(me, from, chan, ctx, db) {
+        return;
+    }
+    let Some(target) = net.uid_by_nick(nick).map(str::to_string) else {
+        ctx.notice(me, from.uid, format!("\x02{nick}\x02 isn't here."));
+        return;
+    };
+    let host = net.host_of(&target).unwrap_or("*");
+    ctx.channel_mode(me, chan, &format!("+b *!*@{host}"));
+    let reason = if args.len() > 3 { args[3..].join(" ") } else { "Banned".to_string() };
+    ctx.kick(me, chan, &target, &reason);
+}