Scaffold the federated services daemon

Protocol-agnostic core: a Protocol trait maps raw server-to-server lines to a
normalized event/action model, so the engine never touches a raw line and a new
ircd is one new module. Adds event-log state (state is a fold over the log) and
a service framework. First protocol impl links to an InspIRCd (insp4) uplink —
completes the CAPAB/SERVER handshake, bursts, and introduces NickServ.

src/services/nickserv.rs

@@ -0,0 +1,25 @@
+use crate::engine::service::{Service, ServiceCtx};
+
+pub struct NickServ {
+    pub uid: String,
+}
+
+impl Service for NickServ {
+    fn nick(&self) -> &str {
+        "NickServ"
+    }
+    fn uid(&self) -> &str {
+        &self.uid
+    }
+    fn gecos(&self) -> &str {
+        "Nickname Services"
+    }
+
+    fn on_command(&mut self, from: &str, args: &[&str], ctx: &mut ServiceCtx) {
+        match args.first().map(|s| s.to_ascii_uppercase()).as_deref() {
+            Some("HELP") => ctx.notice(self.uid(), from, "Commands: REGISTER, IDENTIFY (coming soon)."),
+            Some(other) => ctx.notice(self.uid(), from, format!("Unknown command: {}. Try HELP.", other)),
+            None => {}
+        }
+    }
+}