fix: launch ffmpeg via cmd /k for real console window

scripts/dev-env.ps1

@@ -99,7 +99,11 @@ function Invoke-Start {
         }
     }
     if ($ffArgs) {
-        Start-Detached "ffmpeg" $ffmpeg $ffArgs -Visible
+        $ffPath = (Get-Command $ffmpeg -ErrorAction SilentlyContinue).Source
+        if (-not $ffPath) { $ffPath = $ffmpeg }
+        $ffCmd = "`"$ffPath`" $($ffArgs -join ' ')"
+        Start-Process "cmd" -ArgumentList "/k", $ffCmd
+        Write-Host "  [START] ffmpeg (cmd窗口)" -ForegroundColor Green
     }
 
     # 3. Media server (runs on RK3588, not local)