Refactor AccountForm with 2D code toggle and conditional validation

- Refactor AccountForm to use toggle for showing/hiding profile fields
- Add show2dCodeInMonthlyStatement field to UserProfile database schema
- Implement conditional validation: all fields mandatory when 2D code is enabled
- Update FormSchema with .refine() methods for firstName, lastName, address, and IBAN
- IBAN validation includes both presence check and format validation when required
- Add validation error messages to English and Croatian localization files
- Initialize toggle state from persisted database value
- Form fields conditionally displayed based on toggle state

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

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

app/lib/db-types.ts

@@ -26,6 +26,8 @@ export interface UserProfile {
     address?: string | null;
     /** IBAN */
     iban?: string | null;
+    /** whether to show 2D code in monthly statement */
+    show2dCodeInMonthlyStatement?: boolean | null;
 };
 
 /** bill object in the form returned by MongoDB */