fix(desktop): 动态分配 sidecar 端口替代硬编码，避免端口冲突

使用 net.createServer().listen(0) 探测可用端口，通过 PORT 环境变量
传递给 sidecar binary（VS Code language server 同款模式）

apps/desktop/src/main/index.ts

@@ -1,13 +1,24 @@
 import { spawn } from 'node:child_process'
+import type { AddressInfo } from 'node:net'
+import { createServer } from 'node:net'
 import { join } from 'node:path'
 import { app, BrowserWindow, shell } from 'electron'
 
 const DEV_SERVER_URL = 'http://localhost:3000'
-const PROD_SERVER_PORT = 23_410
 
 let mainWindow: BrowserWindow | null = null
 let serverProcess: ReturnType<typeof spawn> | null = null
 
+const getAvailablePort = (): Promise<number> =>
+  new Promise((resolve, reject) => {
+    const server = createServer()
+    server.listen(0, () => {
+      const { port } = server.address() as AddressInfo
+      server.close(() => resolve(port))
+    })
+    server.on('error', reject)
+  })
+
 const isServerReady = async (url: string): Promise<boolean> => {
   try {
     const response = await fetch(url, { method: 'HEAD' })
@@ -29,14 +40,14 @@ const waitForServer = async (
   return false
 }
 
-const spawnServer = (): string => {
+const spawnServer = (port: number): string => {
   const binaryName = process.platform === 'win32' ? 'server.exe' : 'server'
   const binaryPath = join(process.resourcesPath, binaryName)
 
   serverProcess = spawn(binaryPath, [], {
     env: {
       ...process.env,
-      PORT: String(PROD_SERVER_PORT),
+      PORT: String(port),
       HOST: '127.0.0.1',
     },
     stdio: 'pipe',
@@ -54,14 +65,15 @@ const spawnServer = (): string => {
     console.error('Failed to start server:', err)
   })
 
-  return `http://127.0.0.1:${PROD_SERVER_PORT}`
+  return `http://127.0.0.1:${port}`
 }
 
-const getServerUrl = (): string => {
+const getServerUrl = async (): Promise<string> => {
   if (!app.isPackaged) {
     return DEV_SERVER_URL
   }
-  return spawnServer()
+  const port = await getAvailablePort()
+  return spawnServer(port)
 }
 
 const createWindow = async () => {
@@ -87,7 +99,7 @@ const createWindow = async () => {
   }
   mainWindow.show()
 
-  const serverUrl = getServerUrl()
+  const serverUrl = await getServerUrl()
 
   console.log(`Waiting for server at ${serverUrl}...`)
   const ready = await waitForServer(serverUrl)