Expand OperServ: SQLINE nick bans, GLOBAL, and KILL

Generalise the network-ban store to carry the ircd X-line kind (defaulted
to the user@host G-line for existing records) so one event-sourced,
lazily-expiring, burst-reasserted list backs every ban type, and drive
ADD/DEL/LIST from one implementation per kind:

- AKILL stays the user@host G-line; SQLINE is a nick Q-line, its mask
  validated as a nick glob (an @ is refused so an AKILL-shaped mask can't
  become an over-broad nick ban). Both are keyed by (kind, mask).
- GLOBAL <message> announces to every user via a $* server-glob notice.
- KILL <nick> [reason] disconnects a user, attributed to the operator.

All four are admin-gated, and OperServ itself stays invisible to non-opers.
Bans and kills go out as typed actions (AddLine/DelLine/KillUser) the ircd
link serialises to ADDLINE/DELLINE/KILL.

operserv/src/kill.rs

@@ -0,0 +1,21 @@
+use fedserv_api::{NetView, Priv, Sender, ServiceCtx};
+
+// KILL <nick> [reason]: disconnect a user from the network. Admin-only.
+pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, net: &dyn NetView) {
+    if !from.privs.has(Priv::Admin) {
+        ctx.notice(me, from.uid, "Access denied — KILL needs the \x02admin\x02 privilege.");
+        return;
+    }
+    let Some(&target) = args.get(1) else {
+        ctx.notice(me, from.uid, "Syntax: KILL <nick> [reason]");
+        return;
+    };
+    let Some(uid) = net.uid_by_nick(target).map(str::to_string) else {
+        ctx.notice(me, from.uid, format!("There's no \x02{target}\x02 online."));
+        return;
+    };
+    let by = from.account.unwrap_or(from.nick);
+    let reason = if args.len() > 2 { args[2..].join(" ") } else { "No reason given".to_string() };
+    ctx.kill(me, &uid, &format!("({by}) {reason}"));
+    ctx.notice(me, from.uid, format!("\x02{target}\x02 has been disconnected."));
+}