Replace manual "type the number and order ID" flow with:
- Client-side QR code (qrcode npm package) for desktop users
- Pre-filled Swish payment URL (app.swish.nu) for mobile users
- Manual number fallback + "Jag har betalat" confirmation
The Swish C2B URL scheme pre-fills amount and message (order ID)
without requiring any Swish Commerce API certificate or bank agreement.
Supports both personal phone numbers (070...) and Swish Företag
business numbers (123...) via number normalization in buildSwishPaymentUrl().
Set SWISH_NUMBER in .env to a Företags number once set up.
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