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/(app)/employees/page.tsx

@@ -42,7 +42,7 @@ export default async function EmployeesPage({ searchParams }: EmployeesPageProps
   let query = supabase
     .from("employees")
     .select(
-      "id, first_name, last_name, personnel_number, job_title, team_id, division_id, location_id, entry_date, employment_type, weekly_hours, status",
+      "id, first_name, last_name, personnel_number, job_title, team_id, division_id, location_id, entry_date, employment_type, weekly_hours, status, absence_type",
       { count: "exact" }
     )
     .order("last_name", { ascending: true })
@@ -130,7 +130,7 @@ export default async function EmployeesPage({ searchParams }: EmployeesPageProps
                     {e.employment_type} · <span className="tabular-nums">{e.weekly_hours}h</span>
                   </td>
                   <td className="px-4 py-2.5">
-                    <StatusChip status={e.status} entryDate={e.entry_date} />
+                    <StatusChip status={e.status} entryDate={e.entry_date} absenceType={e.absence_type} />
                   </td>
                 </tr>
               );