Supp/invoice bfl errors (#390)

* feat(accounting): update accounting method validation and messaging for aktiebolag and enskild firma

* Remove AI subsystem and related code

- Deleted AI proposals and requests persistence logic from `lib/ai/proposals/persist.ts`.
- Removed re-validation logic for proposals in `lib/ai/proposals/re-validate.ts`.
- Cleaned up schemas related to AI flows in `lib/api/schemas.ts`.
- Removed AI-related fields from bookkeeping engine in `lib/bookkeeping/engine.ts`.
- Eliminated AI event types from `lib/events/types.ts`.
- Updated tests to reflect the removal of AI-related functionality in `lib/extensions/__tests__/sectors.test.ts`.
- Adjusted initialization logic in `lib/init.ts` to exclude AI proposal handler registration.
- Cleaned up transaction ingestion logic in `lib/transactions/ingest.ts` to remove AI flow checks.
- Updated helper functions in `tests/helpers.ts` to remove AI-related settings.
- Removed AI-related types and interfaces from `types/index.ts`.
- Added migration script to drop AI-related tables and settings from the database.

* fix(migrations): ensure foreign key constraint is dropped before removing AI tables

* feat(invoice-inbox): implement deterministic invoice field extraction and inbox provisioning

- Added `extract-invoice-fields.ts` for extracting fields from PDF invoices using regex and pdfjs-dist, replacing the previous AI classifier.
- Introduced `inbox-provisioning.ts` to manage company inbox addresses and rotation of inboxes using Supabase RPCs.
- Created `resend-inbound.ts` for handling inbound email events and attachments via the Resend API.
- Defined the extension manifest for the invoice inbox, specifying required environment variables and descriptions.
- Migrated database schema to remove AI-related columns and tighten the status enum in `invoice_inbox_items`.

* feat(invoice-inbox): remove AI-specific columns and tighten status enum

* fix(skattekonto): remove manual entry creation reference from transaction input

* fix(schemas): remove accounting method validation for aktiebolag in UpdateSettingsSchema

components/onboarding/Step4VatAccounting.tsx

@@ -263,11 +263,10 @@ export default function Step4VatAccounting({
                       ? 'Intäkter och kostnader bokförs när fakturan skickas eller tas emot, oavsett när betalningen sker. Detta ger en mer rättvisande bild av verksamhetens ekonomi.'
                       : 'Intäkter och kostnader bokförs först när betalningen faktiskt sker. Enklare att hantera men ger en mindre exakt bild av verksamhetens ekonomi vid varje given tidpunkt.'}
                   </p>
-                  {entityType === 'aktiebolag' && (
-                    <p className="text-xs text-amber-800 dark:text-amber-200 bg-warning/10 rounded px-2 py-1">
-                      Aktiebolag med omsättning över 3 MSEK per år måste använda faktureringsmetoden.
-                    </p>
-                  )}
+                  <p className="text-xs text-amber-800 dark:text-amber-200 bg-warning/10 rounded px-2 py-1">
+                    Kontantmetoden får användas om årlig nettoomsättning normalt är högst
+                    3 MSEK (BFL 5 kap. 2 §).
+                  </p>
                 </div>
               </div>
             </div>