Implement Phase 5: reconciliation, SignalR notifications, payees, splits & plugins

Add full frontend UI for five backend features: bank reconciliation (3-step
stepper workflow), payee management (CRUD with alias chips), transaction splits
(expandable rows + split editor), plugins (card grid), and real-time SignalR
notifications (bell dropdown with badge). Fix backend PayeeResponse to expose
alias IDs for deletion.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/App.vue

@@ -8,9 +8,21 @@
 </template>
 
 <script setup lang="ts">
+import { watch } from 'vue'
 import { useAuthStore } from '@/stores/auth'
+import { useNotifications } from '@/composables/useNotifications'
 import AppLayout from '@/components/layout/AppLayout.vue'
 
 const authStore = useAuthStore()
 authStore.initialize()
+
+const { connect, disconnect } = useNotifications()
+
+watch(() => authStore.isAuthenticated, (authenticated) => {
+  if (authenticated) {
+    connect()
+  } else {
+    disconnect()
+  }
+}, { immediate: true })
 </script>