fix: harden powershell environment scripts

scripts/download_wheels.ps1

@@ -1,7 +1,55 @@
+param(
+  [switch]$NoPause
+)
+
 $ErrorActionPreference = "Stop"
 $Root = Split-Path -Parent $PSScriptRoot
 $WheelDir = Join-Path $Root "vendor\wheels"
 $Req = Join-Path $Root "requirements.txt"
-New-Item -ItemType Directory -Force -Path $WheelDir | Out-Null
-python -m pip download -r $Req -d $WheelDir
-Write-Host "依赖包已下载到 $WheelDir"
+
+function Wait-BeforeExit {
+  if (-not $NoPause) {
+    Write-Host ""
+    Read-Host "Press Enter to exit"
+  }
+}
+
+function Get-PythonCommand {
+  foreach ($name in @("py", "python", "python3")) {
+    if (Get-Command $name -ErrorAction SilentlyContinue) {
+      return $name
+    }
+  }
+  throw "Python was not found. Install Python 3.10+ before downloading wheels."
+}
+
+try {
+  Set-Location $Root
+  if (-not (Test-Path $Req)) {
+    throw "requirements.txt was not found: $Req"
+  }
+
+  $python = Get-PythonCommand
+  New-Item -ItemType Directory -Force -Path $WheelDir | Out-Null
+
+  Write-Host "Downloading offline wheels to: $WheelDir" -ForegroundColor Cyan
+  if ($python -eq "py") {
+    & py -3 -m pip download -r $Req -d $WheelDir
+  } else {
+    & $python -m pip download -r $Req -d $WheelDir
+  }
+
+  if ($LASTEXITCODE -ne 0) {
+    throw "Wheel download failed. Check network access and pip."
+  }
+
+  Write-Host ""
+  Write-Host "Offline wheels downloaded. Copy the whole project folder to the server and run scripts\install_offline.ps1." -ForegroundColor Green
+} catch {
+  Write-Host ""
+  Write-Host "Download failed:" -ForegroundColor Red
+  Write-Host $_.Exception.Message -ForegroundColor Red
+  exit 1
+} finally {
+  Wait-BeforeExit
+}