Add "none" option for proof of payment type

Enhanced the proof of payment attachment feature with the following improvements:

- Renamed field from `proofOfPaymentAttachmentType` to `proofOfPaymentType` for consistency
- Added "none" option allowing users to disable proof of payment attachments
- Changed default value from "combined" to "none" for better UX
- Repositioned section in form after payment instructions (more logical flow)
- Added conditional warning when "combined" is selected without payment method
- Updated translations with emojis and improved tooltips for all options
- Backend validation and database operations updated to support new field structure

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/lib/db-types.ts

@@ -56,7 +56,7 @@ export interface BillingLocation {
     tenantPaymentMethod?: "none" | "iban" | "revolut" | null;
 
     /** (optional) type of proof of payment attachment */
-    proofOfPaymentAttachmentType: "combined" | "per-bill";
+    proofOfPaymentType: "none" | "combined" | "per-bill";
 
     /** (optional) tenant name */
     tenantName?: string | null;