feat(desktop): surface runtime alerts as system notifications

Add a runtime system notifier that pushes danger-severity activity (and
forced account-access alerts) to the OS via the tray balloon on Windows,
falling back to Electron Notification elsewhere, with a 30s per-key
dedupe window. Route risk-control / human-verification account alerts
through it so users are notified when an account needs attention.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/desktop-client/src/main/tray.ts

@@ -1,6 +1,6 @@
 import { nativeImage } from 'electron/common'
 import type { Tray as ElectronTray } from 'electron/main'
-import { Menu, Tray } from 'electron/main'
+import { Menu, Notification, Tray } from 'electron/main'
 
 import { TRAY_DANGER_ICON_BASE64, TRAY_ICON_BASE64, TRAY_WINDOWS_ICON_BASE64 } from './brand-icons'
 
@@ -52,12 +52,12 @@ function formatIssueCount(count: number): string {
 // Windows-only: tray.displayBalloon shows a system toast next to the tray
 // icon. macOS and Linux ignore this call (Electron returns silently), so the
 // guard here is just to avoid the no-op log noise on non-Windows.
-export function showTrayBalloon(title: string, content: string): void {
+function displayTrayBalloon(title: string, content: string): boolean {
   if (process.platform !== 'win32') {
-    return
+    return false
   }
   if (!tray || tray.isDestroyed()) {
-    return
+    return false
   }
   try {
     tray.displayBalloon({
@@ -66,11 +66,38 @@ export function showTrayBalloon(title: string, content: string): void {
       icon: createTrayIcon('normal'),
       iconType: 'custom',
     })
+    return true
   } catch (error) {
     console.warn('[desktop-tray] displayBalloon failed', error)
+    return false
   }
 }
 
+export function showTrayBalloon(title: string, content: string): void {
+  displayTrayBalloon(title, content)
+}
+
+export function showSystemNotification(title: string, body: string): void {
+  const normalizedTitle = title.trim()
+  const normalizedBody = body.trim()
+  if (!normalizedTitle || !normalizedBody) {
+    return
+  }
+  if (displayTrayBalloon(normalizedTitle, normalizedBody)) {
+    return
+  }
+  if (!Notification.isSupported()) {
+    return
+  }
+
+  const notification = new Notification({
+    title: normalizedTitle,
+    body: normalizedBody,
+    silent: false,
+  })
+  notification.show()
+}
+
 export function updateTrayIssueIndicator(issueCount: number): void {
   if (!tray || tray.isDestroyed()) {
     return