Implement Phase 6: automated bank sync (Plaid + SimpleFIN) & settings

Add automated transaction syncing via Plaid and SimpleFIN providers,
a Settings page for managing connections and account mappings,
background scheduled syncing, and sync history logging.

New backend: BankSync plugin project with PlaidSyncProvider and
SimpleFinSyncProvider, SyncConnection/LinkedAccount/SyncLog models,
AES-256 encryption service, BankSyncService orchestration,
BankSyncBackgroundService (15-min tick), and BankSyncController
(13 endpoints). EF migration creates sync_connections,
linked_accounts, and sync_logs tables.

New frontend: Settings view with 3 tabs (Profile, Bank Connections,
Sync History), bankSync API service, BankSyncComplete SignalR
notifications, and Settings nav item in sidebar + avatar dropdown.

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

frontend/src/composables/useNotifications.ts

@@ -1,7 +1,7 @@
 import { ref, computed } from 'vue'
 import { HubConnectionBuilder, HubConnection, LogLevel } from '@microsoft/signalr'
 import { useAuthStore } from '@/stores/auth'
-import type { AppNotification, FileImportNotification } from '@/types'
+import type { AppNotification, FileImportNotification, BankSyncNotification } from '@/types'
 
 const notifications = ref<AppNotification[]>([])
 const isConnected = ref(false)
@@ -32,6 +32,16 @@ function connect() {
     })
   })
 
+  connection.on('BankSyncComplete', (data: BankSyncNotification) => {
+    notifications.value.unshift({
+      id: crypto.randomUUID(),
+      type: 'BankSyncComplete',
+      data,
+      timestamp: new Date().toISOString(),
+      read: false
+    })
+  })
+
   connection.onclose(() => {
     isConnected.value = false
   })