feat(salary): repay utlägg with the salary as a tax-free payslip line (#2361)

* feat(salary): repay utlägg with the salary as a tax-free payslip line (#2331)

- expense_reimbursement line type: kostnadsersättning outside gross, tax,
  avgifter and the AGI. The engine adds tax-free reimbursements (utlägg,
  skattefritt traktamente, skattefri milersättning) to the net payout only.
- booking debits the claim's liability account (2820) on top of gross,
  never a 7xxx cost; a run that only repays utlägg posts 2820 D / 1930 K
  instead of being treated as a nollkörning
- salary_line_items.source_expense_claim_id (tenant-scoped FK, cascade,
  one payslip line per claim); settle_expense_claims_via_salary_run marks
  the claims paid with an expense_payout_batches row pointing at the
  salary verifikat, no second verifikat, idempotent on retry; wired into
  bookLoadedRun and the v1 book route with a pre-check before posting
- create_expense_payout_batch refuses claims scheduled on a payslip
  (ON_PAYSLIP); deleteExpenseClaim refuses once the run has left draft
- "Lägg till utlägg" on the employee row of a draft run; the payslip page
  labels and removes the lines
- pg-real: tests/pg/utlagg-via-lon.pg.test.ts + ON_PAYSLIP case

Claude-Session: https://claude.ai/code/session_01LvMaHcTnwAfxzgYD1fGYX1
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* fix(salary): PR #2361 review: claim delete cannot cascade into a booked payslip; AGI excludes the utlägg line

- salary_line_items_source_expense_claim_fkey is ON DELETE RESTRICT (edited
  in the unmerged 20260906210300): the database refuses to delete a claim a
  payslip line still references, whichever path issues the DELETE
- deleteExpenseClaim removes the draft line first (before the storno) and
  keeps refusing with ON_PAYSLIP once the run has left draft
- pg-real: delete refused with 23503 on a booked and on a draft run; the
  app order (line, then claim) succeeds
- unit: AGI builder keeps FK011/FK001/FK487 and emits no benefit field for
  an expense_reimbursement line (FK011 derives from sre.gross_salary; only
  benefit_* types are read from line items)

Claude-Session: https://claude.ai/code/session_01LvMaHcTnwAfxzgYD1fGYX1
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

---------

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

types/index.ts

@@ -4078,6 +4078,7 @@ export type SalaryLineItemType =
   | 'vab' | 'parental_leave' | 'unpaid_leave' | 'vacation' | 'semesterersattning'
   | 'traktamente_taxfree' | 'traktamente_taxable'
   | 'mileage_taxfree' | 'mileage_taxable'
+  | 'expense_reimbursement'
   | 'net_deduction_advance' | 'net_deduction_union' | 'net_deduction_benefit_payment'
   | 'net_deduction_other'
   | 'oresavrundning'
@@ -4273,6 +4274,8 @@ export interface SalaryLineItem {
   is_net_deduction: boolean
   account_number: string | null
   sort_order: number
+  /** The registered utlägg an expense_reimbursement line repays (#2331). */
+  source_expense_claim_id?: string | null
   created_at: string
   updated_at: string
 }