asked the clanker to change the arcidecture a bit

crates/services/src/lib.rs

@@ -0,0 +1,14 @@
+//! Service registry: turns a route key into the subscription that backs it.
+//! Adding a service is a new crate under `crates/services/` plus one arm in
+//! `subscription` — core never changes.
+
+use iced::Subscription;
+
+use common::{Service, ServicePayloadKind};
+
+/// The subscription backing a route key.
+pub fn subscription(service: &Service) -> Subscription<ServicePayloadKind> {
+    match service {
+        Service::Clock(_) => service_datetime::ClockTicker::run(),
+    }
+}