refactor: replace payment dropdown with independent toggles

- Replace showPaymentInstructionsInMonthlyStatement dropdown with enableIbanPayment and enableRevolutPayment boolean toggles
- Update UserSettingsForm to use separate fieldsets for IBAN and Revolut with independent toggle switches
- Add hidden inputs to preserve values when toggles are disabled
- Update validation logic to check enableIbanPayment instead of show2dCodeInMonthlyStatement
- Reorganize translation keys to match new structure (iban-* and revolut-* prefixes)
- Update ViewLocationCard to use enableIbanPayment field

This provides better UX by allowing users to enable both payment methods simultaneously if needed.

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

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

app/lib/db-types.ts

@@ -18,6 +18,8 @@ export interface YearMonth {
 export interface UserSettings {
     /** user's ID */
     userId: string;
+    /** whether enableshow IBAN payment instructions in monthly statement */
+    enableIbanPayment?: boolean | null;
     /** owner name */
     ownerName?: string | null;
     /** owner street */
@@ -28,18 +30,10 @@ export interface UserSettings {
     ownerIBAN?: string | null;
     /** currency (ISO 4217) */
     currency?: string | null;
+    /** whether to enable Revolut payment instructions in monthly statement */
+    enableRevolutPayment?: boolean | null;
     /** owner Revolut payment link */
     ownerRevolutProfileName?: string | null;
-    /** whether to show 2D code in monthly statement */
-    show2dCodeInMonthlyStatement?: boolean | null;
-    /** whether to  show payment instructions in monthly statement */
-    showPaymentInstructionsInMonthlyStatement?: "disabled" | "iban" | "revolut" | null;
-
-    // /** whether enableshow IBAN payment instructions in monthly statement */
-    // enableIbanPaymentInstructionsInMonthlyStatement?: boolean | null;
-    // /** whether to enable Revolut payment instructions in monthly statement */
-    // enableRevolutPaymentInstructionsInMonthlyStatement?: boolean | null;
-    
 };
 
 /** bill object in the form returned by MongoDB */