Add OperServ with AKILL network bans

The first operator module. AKILL manages network bans as a typed,
event-sourced list with lazy expiry, mirroring the patterns the other
modules use:

- AKILL ADD [+expiry] <user@host> <reason> stores the ban and drives an
  ircd G-line (applied to matching users already online and to future
  connections); AKILL DEL <mask|number> lifts it; AKILL LIST [pattern]
  shows the live list, numbered. Admin-only.
- Bans are Global events, so every node holds the list and re-asserts each
  one at burst with its remaining duration. Expired bans are hidden lazily
  and dropped at compaction.
- Masks are normalised to user@host (a nick! prefix is stripped, both
  sides lowercased) and an all-wildcard mask is refused.

Email (send_email) is already reachable from the api via ServiceCtx, and
adds AddLine/DelLine to the action vocabulary for any future X-line kinds.

operserv/src/lib.rs

@@ -0,0 +1,45 @@
+//! OperServ gives services operators network-wide tools. The first is AKILL:
+//! network bans (G-lines) that keep matching users off the whole network,
+//! event-sourced so they survive a restart and re-apply at burst, with lazy
+//! expiry like the rest of the store. `lib.rs` dispatches; each command is its
+//! own file.
+
+use fedserv_api::{NetView, Sender, Service, ServiceCtx, Store};
+
+#[path = "akill.rs"]
+mod akill;
+
+pub struct OperServ {
+    pub uid: String,
+}
+
+impl Service for OperServ {
+    fn nick(&self) -> &str {
+        "OperServ"
+    }
+    fn uid(&self) -> &str {
+        &self.uid
+    }
+    fn gecos(&self) -> &str {
+        "Operator Service"
+    }
+
+    fn on_command(&mut self, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, _net: &dyn NetView, db: &mut dyn Store) {
+        let me = self.uid.as_str();
+        // Every OperServ command is operator-only: reveal nothing to others.
+        if !from.privs.any() {
+            ctx.notice(me, from.uid, "Access denied — OperServ is for services operators.");
+            return;
+        }
+        match args.first().copied() {
+            Some(cmd) if cmd.eq_ignore_ascii_case("AKILL") => akill::handle(me, from, args, ctx, db),
+            Some(cmd) if cmd.eq_ignore_ascii_case("HELP") => help(me, from, ctx),
+            None => help(me, from, ctx),
+            Some(other) => ctx.notice(me, from.uid, format!("I don't know \x02{other}\x02. Try \x02AKILL\x02 or \x02HELP\x02.")),
+        }
+    }
+}
+
+fn help(me: &str, from: &Sender, ctx: &mut ServiceCtx) {
+    ctx.notice(me, from.uid, "OperServ holds network operator tools. \x02AKILL ADD\x02 [+expiry] <user@host> <reason>, \x02AKILL DEL\x02 <user@host|number>, \x02AKILL LIST\x02 [pattern] — network bans (Priv::Admin).");
+}