feat(desktop): native desktop enhancements

- Add a minimal application menu with common items and shortcuts:
  New Chat (Cmd+N), Settings (Cmd+,), Reload, etc.
- Add system tray with show window, new chat, and quit; click icon to restore
- Add single-instance lock so relaunching focuses the existing window
- Implement close-to-tray: closing the window hides it; only a real quit destroys it
- Explicitly define Window menu's Close Window bound to Cmd+W / Ctrl+W to reliably trigger hide-to-tray
- Listen for menu-action in the renderer to handle menu-triggered new chat / open settings

desktop/src/renderer/src/App.tsx

@@ -1,5 +1,5 @@
 import React, { useState, useCallback, useEffect } from 'react'
-import { Routes, Route, useLocation } from 'react-router-dom'
+import { Routes, Route, useLocation, useNavigate } from 'react-router-dom'
 import { PanelLeftOpen } from 'lucide-react'
 import NavRail from './layout/NavRail'
 import SessionList from './layout/SessionList'
@@ -8,6 +8,7 @@ import StatusScreen from './components/StatusScreen'
 import { useBackend } from './hooks/useBackend'
 import { usePlatform } from './hooks/usePlatform'
 import { useUIStore } from './store/uiStore'
+import { useSessionStore } from './store/sessionStore'
 import apiClient from './api/client'
 import { t } from './i18n'
 import ChatPage from './pages/ChatPage'
@@ -22,6 +23,7 @@ import LogsPage from './pages/LogsPage'
 const App: React.FC = () => {
   const backend = useBackend()
   const location = useLocation()
+  const navigate = useNavigate()
   const { isWin } = usePlatform()
   const { sessionsCollapsed, toggleSessions } = useUIStore()
   const [, forceUpdate] = useState(0)
@@ -30,6 +32,18 @@ const App: React.FC = () => {
     if (backend.status === 'ready') apiClient.setBaseUrl(backend.baseUrl)
   }, [backend.status, backend.baseUrl])
 
+  // Handle app-menu / shortcut actions forwarded from the main process.
+  useEffect(() => {
+    window.electronAPI?.onMenuAction?.((action) => {
+      if (action === 'new-chat') {
+        useSessionStore.getState().newSession()
+        navigate('/')
+      } else if (action === 'open-settings') {
+        navigate('/settings')
+      }
+    })
+  }, [navigate])
+
   const handleLangChange = useCallback(() => forceUpdate((n) => n + 1), [])
 
   if (backend.status !== 'ready') {

desktop/src/renderer/src/types.ts

@@ -15,6 +15,7 @@ export interface ElectronAPI {
   windowClose: () => Promise<void>
   windowIsMaximized: () => Promise<boolean>
   onMaximizeChange: (callback: (maximized: boolean) => void) => void
+  onMenuAction?: (callback: (action: string) => void) => void
   platform: string
 }