refactor: convert service callbacks to DbWatch pattern

Convert getServiceInterface, listServiceInterfaces, getSystemSmtp, and
getServiceManifest from manual callback triggers to DbWatchedCallbacks.
getServiceManifest now always returns the installed manifest.

core/src/service/mod.rs

@@ -640,17 +640,6 @@ impl Service {
             tokio::task::yield_now().await;
         }
 
-        // Trigger manifest callbacks after successful installation
-        let manifest = service.seed.persistent_container.s9pk.as_manifest();
-        if let Some(callbacks) = ctx.callbacks.get_service_manifest(&manifest.id) {
-            let manifest_value =
-                serde_json::to_value(manifest).with_kind(ErrorKind::Serialization)?;
-            callbacks
-                .call(imbl::vector![manifest_value.into()])
-                .await
-                .log_err();
-        }
-
         Ok(service)
     }