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.

app/api/export/employees/route.ts

@@ -1,4 +1,5 @@
 import { NextResponse, type NextRequest } from "next/server";
+import { statusLabel } from "@/lib/absence";
 import { exportFilename, exportResponseHeaders, toCsv, toXlsx, type ExportColumn } from "@/lib/export";
 import { deriveStatusAsOf, parseIsoDateParam, parseStatuses, type OrgLookups } from "@/lib/reports";
 import { loadDependentsCounts, loadOrgLookups, type ReportFilters } from "@/lib/reports-data";
@@ -103,12 +104,16 @@ function employeeExportColumns(
     { header: "C-Level", get: (e) => e.is_c_level },
     { header: "Paygrade", get: (e) => e.paygrade },
     { header: "Herkunft", get: (e) => e.source },
-    { header: "Status", get: (e) => e.status },
+    // The export shows the display name, not the raw enum value — a payroll
+    // hand-off saying "Karenz" for what the app calls Langzeitabwesenheit
+    // would just cause questions.
+    { header: "Status", get: (e) => statusLabel(e.status) },
+    { header: "Art der Langzeitabwesenheit", get: (e) => e.absence_type },
     { header: "Eintrittsdatum", get: (e) => e.entry_date, kind: "date" },
     { header: "Austrittsdatum", get: (e) => e.exit_date, kind: "date" },
     { header: "Austrittsgrund", get: (e) => e.exit_reason },
-    { header: "Karenzbeginn", get: (e) => e.karenz_start_date, kind: "date" },
-    { header: "Karenz-Rückkehrdatum", get: (e) => e.karenz_return_date, kind: "date" },
+    { header: "Abwesenheit ab", get: (e) => e.karenz_start_date, kind: "date" },
+    { header: "Rückkehr geplant", get: (e) => e.karenz_return_date, kind: "date" },
     { header: "Anzahl Angehörige", get: (e) => dependentsCounts.get(e.id) ?? 0 },
   ];
   if (asOf) {