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/services/plugins.ts

@@ -0,0 +1,6 @@
+import api from './api'
+import type { Plugin } from '@/types'
+
+export const pluginsApi = {
+  getAll: () => api.get<Plugin[]>('/plugins'),
+}