refactor(auth): decouple auth from push via domain events

Introduce internal/listener as a domain event bus so oauth and user
modules emit AdminLoggedIn without depending on admin/push. Register
push handlers explicitly at the router composition root, replacing
init() side-effect registration and blank imports.

internal/apps/admin/push/custom_events/register.go

@@ -0,0 +1,17 @@
+// Copyright 2026 Arctel.net
+// SPDX-License-Identifier: Apache-2.0
+
+package custom_events
+
+import (
+	"github.com/Rain-kl/Wavelet/internal/apps/admin/push"
+	"github.com/Rain-kl/Wavelet/internal/listener"
+)
+
+// Register wires push notification handlers for domain events and registers
+// built-in event metadata. Must be called once during application bootstrap
+// before push.SyncEvents.
+func Register() {
+	push.RegisterBuiltInEvent(AdminLogin)
+	listener.OnAdminLoggedIn(handleAdminLogin)
+}