Refactor bookkeeping error handling and introduce new error classes (#356)

- Introduced new error classes for better error categorization:
  - JournalEntryNotBalancedError
  - FiscalPeriodNotFoundError
  - EntryDateOutsideFiscalPeriodError
  - JournalEntryNotFoundError
  - CannotReverseNonPostedError
  - CannotCorrectNonPostedError
  - EntryAlreadyReversedError
  - CurrencyRevaluationAlreadyExistsError
  - InvalidMappingResultError
  - BookkeepingDatabaseError

- Updated existing functions in engine.ts and transaction-entries.ts to throw specific errors instead of generic ones.
- Enhanced error response handling in get-error-message.ts to provide localized messages for new error types.
- Added unit tests for new error classes and error handling functions to ensure correctness and coverage.

app/api/import/opening-balance/execute/route.ts

@@ -6,7 +6,7 @@ import { OpeningBalanceExecuteSchema } from '@/lib/api/schemas'
 import { requireWritePermission } from '@/lib/auth/require-write'
 import { requireCompanyId } from '@/lib/company/context'
 import { createJournalEntry } from '@/lib/bookkeeping/engine'
-import { AccountsNotInChartError, accountsNotInChartResponse } from '@/lib/bookkeeping/errors'
+import { bookkeepingErrorResponse } from '@/lib/bookkeeping/errors'
 import { getBASReference } from '@/lib/bookkeeping/bas-reference'
 import { fetchAllRows } from '@/lib/supabase/fetch-all'
 import type { CreateJournalEntryLineInput } from '@/types'
@@ -242,9 +242,8 @@ export async function POST(request: Request) {
       },
     })
   } catch (error) {
-    if (error instanceof AccountsNotInChartError) {
-      return accountsNotInChartResponse(error)
-    }
+    const typed = bookkeepingErrorResponse(error)
+    if (typed) return typed
     console.error('Opening balance execute error:', error)
     return NextResponse.json(
       { error: error instanceof Error ? error.message : 'Importen misslyckades' },