Import improvements

We've made a bunch of improvements to imports, so it's easier to bring in customer data without also bringing in a headache.

You can now:

• choose whether to import balances
• choose whether to import scheduled dates
• turn off customer notifications for that import, instead of changing them in Settings first
• add extra instructions for the AI processing your CSV, handy if your file needs a bit more context
• see the uploaded CSV filename on each import, so it's easier to tell which import used which file

That means more control over what comes in, and a clearer view of what's been imported from where.