Fix backup process in Windows

[shernandezp]

What and why

Checklist

• Targets the develop branch (not master)
• dotnet build and dotnet test pass locally
• Client checks pass (npm run check:i18n, npx tsc -b, npx vitest run) if the client changed
• User-facing text is provided in both Spanish and English
• Docs updated if behaviour or the API changed (docs/, in-product Help, docs/openapi/v1.json)
• No secrets, credentials, or encrypted-folder contents committed