feat: add prompt-first batches and pausable task guidance

scripts/start.ps1

@@ -219,11 +219,16 @@ function Install-PortableScrcpy {
 
     Write-Host "   [INFO] Installing portable scrcpy in user space..." -ForegroundColor Cyan
     if ($ArtemisDownloads.mode -eq 'China' -and $ArtemisDownloads.scrcpy_url.StartsWith('https://github.com/')) {
-        Write-Host '   [INFO] scrcpy uses GitHub. If unreachable, set overrides.scrcpy_url in config/downloads.json.' -ForegroundColor Yellow
+        Write-Host '   [WARN] China mode has no non-GitHub scrcpy source. Configure overrides.scrcpy_url or install scrcpy manually.' -ForegroundColor Yellow
+        return $false
     }
     try {
         $zipPath = "$env:TEMP\scrcpy-win64.zip"
         if (Invoke-DownloadFile -Uri $ArtemisDownloads.scrcpy_url -OutFile $zipPath) {
+            $actualHash = (Get-FileHash -LiteralPath $zipPath -Algorithm SHA256).Hash.ToLowerInvariant()
+            if ($actualHash -ne $ArtemisDownloads.scrcpy_sha256) {
+                throw 'Downloaded scrcpy ZIP failed official SHA256 verification.'
+            }
             $extractDir = "$env:TEMP\scrcpy_extract"
             if (Test-Path $extractDir) { Remove-Item $extractDir -Recurse -Force -ErrorAction SilentlyContinue }
             New-Item -ItemType Directory -Path $extractDir -Force | Out-Null