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.

supabase/seed.ts

@@ -11,6 +11,7 @@ import { randomUUID } from "node:crypto";
 // Explicit .ts extension: this file is run directly by Node (type-stripping,
 // ESM), where an extensionless relative import does not resolve.
 import { svnrCheckDigit } from "../lib/svnr.ts";
+import { ABSENCE_TYPES } from "../lib/absence.ts";
 
 const SUPABASE_URL = process.env.NEXT_PUBLIC_SUPABASE_URL;
 const SERVICE_ROLE_KEY = process.env.SUPABASE_SERVICE_ROLE_KEY;
@@ -344,7 +345,9 @@ type EmployeeRow = {
   entry_date: string;
   exit_date: string | null;
   exit_reason: string | null;
+  karenz_start_date: string | null;
   karenz_return_date: string | null;
+  absence_type: string | null;
 };
 
 type HistoryRow = {
@@ -460,7 +463,9 @@ function finalizeEmployee(base: ReturnType<typeof newHireBase>, opts: { paygrade
     entry_date: isoDate(entryDate),
     exit_date: null,
     exit_reason: null,
+    karenz_start_date: null,
     karenz_return_date: null,
+    absence_type: null,
   };
 
   history.push({
@@ -578,19 +583,23 @@ for (let i = 0; i < 40 && cursor < shuffledIcs.length; i++, cursor++) {
   history.push({ employee_id: e.id, event_date: e.exit_date, event_type: "Austritt", description: `Austritt (${e.exit_reason})` });
 }
 
-// ~12 Karenz
+// ~12 Langzeitabwesenheiten, über die Arten gestreut statt alle als Karenz —
+// die Auswertung nach Art ist sonst nicht zu sehen.
 for (let i = 0; i < 12 && cursor < shuffledIcs.length; i++, cursor++) {
   const e = shuffledIcs[cursor];
   const entryDate = new Date(e.entry_date);
   const karenzStart = randomDateBetween(addDays(entryDate, 180), addDays(TODAY, -10));
   const returnDate = addDays(TODAY, randInt(10, 300));
+  const absenceType = pick(ABSENCE_TYPES);
   e.status = "Karenz";
+  e.karenz_start_date = isoDate(karenzStart);
   e.karenz_return_date = isoDate(returnDate);
+  e.absence_type = absenceType;
   history.push({
     employee_id: e.id,
     event_date: isoDate(karenzStart),
     event_type: "Karenz",
-    description: `Karenzantritt, geplante Rückkehr am ${isoDate(returnDate)}`,
+    description: `${absenceType}, geplante Rückkehr am ${isoDate(returnDate)}`,
   });
 }