Add/csv import options (#420)

* feat(import): add customer and supplier parsing functionality

- Implemented customer file parsing in `lib/import/customers/parser.ts` with support for Excel and CSV formats.
- Created types for detected customer columns and parsed customer rows in `lib/import/customers/types.ts`.
- Added tests for customer classification logic in `lib/import/shared/__tests__/classify.test.ts`.
- Developed classification functions for customers and suppliers in `lib/import/shared/classify.ts`.
- Introduced shared column utility functions in `lib/import/shared/column-utils.ts`.
- Implemented supplier file parsing in `lib/import/suppliers/parser.ts` with validation for various fields.
- Created types for detected supplier columns and parsed supplier rows in `lib/import/suppliers/types.ts`.
- Added tests for supplier column detection and parsing in `lib/import/suppliers/__tests__/column-detector.test.ts` and `lib/import/suppliers/__tests__/parser.test.ts`.

* fix(labels): update 'Svenskt företag' to 'Svenskt företag eller organisation' for clarity

* feat(import): refactor encoding handling for Swedish files and add tests for character preservation

* feat(recapt): implement clearRecaptIdentity function and integrate into logout flow

* feat(bookkeeping): implement copy functionality and next voucher sequence retrieval

* feat(import): enhance customer and supplier import functionality with normalization and event handling

lib/errors/structured-errors.ts

@@ -845,6 +845,44 @@ const OPENING_BALANCE_IMPORT: Record<string, StructuredErrorEntry> = {
   },
 }
 
+const REGISTER_IMPORT: Record<string, StructuredErrorEntry> = {
+  REG_IMPORT_NO_FILE: {
+    httpStatus: 400,
+    message_sv: 'Ingen fil bifogad.',
+    message_en: 'No file attached.',
+  },
+  REG_IMPORT_FILE_TOO_LARGE: {
+    httpStatus: 400,
+    message_sv: 'Filen är för stor. Maxstorlek är 10 MB.',
+    message_en: 'File exceeds the 10 MB size limit.',
+  },
+  REG_IMPORT_INVALID_FORMAT: {
+    httpStatus: 400,
+    message_sv: 'Filformatet stöds inte. Tillåtna format: .xlsx, .xls, .csv, .ods.',
+    message_en: 'Unsupported file format.',
+  },
+  REG_IMPORT_INVALID_COLUMN_OVERRIDES: {
+    httpStatus: 400,
+    message_sv: 'Ogiltig kolumnmappning.',
+    message_en: 'Invalid column overrides JSON.',
+  },
+  REG_IMPORT_PARSE_FAILED: {
+    httpStatus: 500,
+    message_sv: 'Kunde inte tolka filen.',
+    message_en: 'Failed to parse the register file.',
+  },
+  REG_IMPORT_NO_ROWS: {
+    httpStatus: 400,
+    message_sv: 'Inga giltiga rader hittades i filen.',
+    message_en: 'No valid rows found in the file.',
+  },
+  REG_IMPORT_EXECUTE_FAILED: {
+    httpStatus: 500,
+    message_sv: 'Importen misslyckades.',
+    message_en: 'Register import failed.',
+  },
+}
+
 // ─────────────────────────────────────────────────────────────────
 // Wave 3 tail: provider migration extension codes
 // ─────────────────────────────────────────────────────────────────
@@ -1238,6 +1276,7 @@ const REGISTRY: Record<string, StructuredErrorEntry> = {
   ...SIE_IMPORT,
   ...BANK_FILE,
   ...OPENING_BALANCE_IMPORT,
+  ...REGISTER_IMPORT,
   ...PROVIDER_MIGRATION,
   ...DOCUMENT,
   ...CUSTOMER,