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.

components/ui/StatusChip.tsx

@@ -1,3 +1,4 @@
+import { absenceLabel } from "@/lib/absence";
 import { STATUS_STYLES } from "@/lib/colors";
 import { fmtDate } from "@/lib/format";
 import type { EmploymentStatus } from "@/lib/supabase/types";
@@ -5,10 +6,14 @@ import type { EmploymentStatus } from "@/lib/supabase/types";
 type StatusChipProps = {
   status: EmploymentStatus;
   entryDate?: string | null; // shown as "Eintritt {date}" when status is Geplant
+  /** Shown instead of the generic label when the kind of absence is known. */
+  absenceType?: string | null;
 };
 
-export function StatusChip({ status, entryDate }: StatusChipProps) {
-  const label = status === "Geplant" && entryDate ? `Eintritt ${fmtDate(entryDate)}` : status;
+export function StatusChip({ status, entryDate, absenceType }: StatusChipProps) {
+  // The stored status is still 'Karenz'; absenceLabel maps it to
+  // "Langzeitabwesenheit", or to the specific kind when one is recorded.
+  const label = status === "Geplant" && entryDate ? `Eintritt ${fmtDate(entryDate)}` : absenceLabel(status, absenceType);
   return (
     <span
       className={`inline-flex items-center whitespace-nowrap rounded-full px-2.5 py-0.5 text-xs font-semibold ${STATUS_STYLES[status]}`}