Rename Karenz to Langzeitabwesenheit and record its type

Karenz was doing duty as the name for every kind of extended absence, but
the cases behave differently in payroll and reporting — Wochenhilfe, a
Präsenzdienst, a long sick leave and a sabbatical are not the same thing.
The concept is now called Langzeitabwesenheit and carries which kind it is.

- employees.absence_type, constrained to the thirteen kinds. start_karenz
  stores it on both paths (written straight away, or parked in the
  pending_org_changes payload when the absence starts later);
  record_karenz_return and the karenz_return branch of
  apply_due_pending_changes clear it, so a returned employee does not keep
  looking like they are still away. It also reaches employee_history, the
  audit log and the employee export.
- The status enum value stays 'Karenz'. Postgres can rename an enum value in
  place, but every stored function body that spells it would then reference
  a value that no longer exists — a dozen functions across fifteen
  migrations, rewritten for a label. The mapping lives in lib/absence.ts
  instead, which is the single place the UI reads the display name from.
- Where a kind is recorded the chip shows it — "Bildungskarenz" says more
  than "Langzeitabwesenheit". Absences predating the field have none and
  fall back to the generic name rather than to a guess, and a value outside
  the list is dropped rather than echoed into the UI.
- The export prints the display name, not the raw enum: a payroll hand-off
  reading "Karenz" for what the app calls Langzeitabwesenheit only causes
  questions. Audit filter options keep their stored values and change only
  their labels.
- The seed spreads the twelve absences across the kinds; all of them being
  Karenz would leave any breakdown by kind invisible.

lib/absence.ts

@@ -0,0 +1,53 @@
+import type { EmploymentStatus } from "./supabase/types";
+
+// Langzeitabwesenheit.
+//
+// The database still stores the employment status as 'Karenz' — renaming an
+// enum value would mean rewriting every stored function that spells it, for
+// a label change (see supabase/migrations/*_absence_type.sql). So the value
+// is mapped to its display name here, in the one place the UI reads it from.
+
+export const ABSENCE_TYPES = [
+  "Wochenhilfe (Mutterschutz)",
+  "Elternkarenz (inkl. Väterkarenz)",
+  "Papamonat",
+  "Bildungskarenz",
+  "Bildungsteilzeit",
+  "Präsenzdienst",
+  "Zivildienst",
+  "Langer Krankenstand",
+  "Wiedereingliederungsteilzeit",
+  "Pflegekarenz",
+  "Pflegeteilzeit",
+  "Familienhospizkarenz",
+  "Sabbatical",
+] as const;
+
+export type AbsenceType = (typeof ABSENCE_TYPES)[number];
+
+export function isAbsenceType(value: string | null | undefined): value is AbsenceType {
+  return ABSENCE_TYPES.includes(value as AbsenceType);
+}
+
+/** Display names for the stored status values. */
+const STATUS_LABELS: Record<EmploymentStatus, string> = {
+  Aktiv: "Aktiv",
+  Karenz: "Langzeitabwesenheit",
+  Geplant: "Geplant",
+  Ausgetreten: "Ausgetreten",
+};
+
+export function statusLabel(status: EmploymentStatus): string {
+  return STATUS_LABELS[status] ?? status;
+}
+
+/**
+ * The chip and the detail header show the specific kind when it is known —
+ * "Bildungskarenz" says more than "Langzeitabwesenheit". Absences recorded
+ * before the type existed have none, and fall back to the generic name
+ * rather than to a guess.
+ */
+export function absenceLabel(status: EmploymentStatus, absenceType: string | null | undefined): string {
+  if (status !== "Karenz") return statusLabel(status);
+  return isAbsenceType(absenceType) ? absenceType : STATUS_LABELS.Karenz;
+}