Feat/voucher docs (#664)

* feat: implement inbox document picker and linking functionality

* feat: implement self-billing invoice functionality

- Added support for registering self-billed invoices received from customers.
- Updated the invoice schema to include fields for self-billing metadata such as `is_self_billed`, `external_invoice_number`, `self_billing_agreement_ref`, and `received_date`.
- Created API route for handling self-billed invoice submissions, including validation and error handling.
- Implemented database migrations to add necessary columns and constraints for self-billing invoices.
- Developed tests to ensure correct behavior of self-billing invoice creation and validation rules.
- Updated Swedish localization files to include new terms related to self-billing.

* feat: enforce SIE import requirement for non-Fortnox providers in migration process

* feat: streamline invoice processing and enhance error logging across APIs

components/dashboard/WelcomeOnboarding.tsx

@@ -208,11 +208,7 @@ export default function WelcomeOnboarding({
         let title = t('toast_error_title')
         let description: string = result.error || t('toast_create_failed')
         let backToStep2 = false
-        if (result.error === 'org_number_exists') {
-          title = t('toast_company_exists_title')
-          description = t('toast_company_exists_description', { appName: branding.appName.toLowerCase() })
-          backToStep2 = true
-        } else if (result.error === 'org_number_invalid') {
+        if (result.error === 'org_number_invalid') {
           title = t('toast_org_invalid_title')
           description = t('toast_org_invalid_description')
           backToStep2 = true