Move the part-time arrangements out of the absence list

Bildungsteilzeit, Elternteilzeit, Pflegeteilzeit and
Wiedereingliederungsteilzeit were offered as kinds of long-term absence.
Recorded that way, the person counted as absent: they dropped out of
headcount, their reporting line fell to a stand-in, and reports stopped
counting them — while they were in the building every week, just for
fewer hours. A part-time arrangement is not an absence; it is a change
of hours.

They now sit where they belong. Wiedereingliederungs- and Elternteilzeit
appear when recording a return from absence, as the reason someone comes
back on reduced hours — both typically begin exactly when the absence
ends. Bildungs- and Pflegeteilzeit appear under "Daten ändern" beside
the hours, next to the ordinary contractual change.

The reason is recorded with the change, not as a state on the person. A
state would have to be maintained, and nobody goes back to note when a
Bildungsteilzeit ended; a field that quietly goes stale is worse than
none. In the history it stands next to the value it explains, and stays
readable for good.

The check constraint on absence_type is deliberately untouched. Three
people carry the old values right now — two Pflegeteilzeit, one
Wiedereingliederungsteilzeit. Forbidding them would make existing rows
illegal. They are gone from the list of choices; the history stays
readable. Those three are worth revisiting, but that is a data decision,
not a code one.

Rehearsed against real data: an hours change with a reason and one
without, a reduced return with a reason and an unchanged one — checked
by reading both new history rows rather than "the latest", since now()
stands still inside a transaction and made an earlier probe report a
false negative.

I also overwrote tests/unit/absence.test.ts instead of extending it. The
original cases are restored; the diff is 49 added lines and 3 changed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

components/employees/panels/DatenAendernPanel.tsx

@@ -13,6 +13,7 @@ import { Field, SelectField, TextField } from "@/components/ui/Field";
 import { SlideOver } from "@/components/ui/SlideOver";
 import { useToast } from "@/components/ui/Toast";
 import { UN_COUNTRIES } from "@/lib/countries";
+import { STUNDEN_GRUENDE } from "@/lib/absence";
 import { fmtFullName, todayIso } from "@/lib/format";
 import { isValidSvnr, requiresAustrianSvnr } from "@/lib/svnr";
 import { EMERGENCY_RELATIONS, type ContractType, type Database, type EmploymentType, type GenderType } from "@/lib/supabase/types";
@@ -64,6 +65,11 @@ export function DatenAendernPanel({
 
   const [employmentType, setEmploymentType] = useState<EmploymentType>(employee.employment_type);
   const [weeklyHours, setWeeklyHours] = useState(String(employee.weekly_hours));
+  // Der Grund wird erst gefragt, wenn sich die Stunden tatsächlich ändern —
+  // sonst stünde bei jeder Adressänderung eine Frage im Weg, die niemand
+  // gestellt hat.
+  const [stundenGrund, setStundenGrund] = useState<string>(STUNDEN_GRUENDE[0]);
+  const stundenGeaendert = Number(weeklyHours) !== Number(employee.weekly_hours);
   const [contractType, setContractType] = useState<ContractType>(employee.contract_type);
   const [contractEndDate, setContractEndDate] = useState(employee.contract_end_date ?? "");
 
@@ -134,6 +140,10 @@ export function DatenAendernPanel({
         emergency_contact_phone: notfallTelefon.trim(),
         emergency_contact_relation: notfallVerhaeltnis.trim(),
       },
+      // Nur mitschicken, wenn sich die Stunden wirklich ändern — sonst
+      // stünde bei jeder Adressänderung ein Grund in der Historie, den
+      // niemand gemeint hat.
+      hours_reason: stundenGeaendert ? stundenGrund : undefined,
       contract: {
         employment_type: employmentType,
         weekly_hours: Number(weeklyHours),
@@ -268,6 +278,16 @@ export function DatenAendernPanel({
               disabled={employmentType === "Vollzeit"}
               onChange={setWeeklyHours}
             />
+            {stundenGeaendert && (
+              <SelectField
+                label="Grund der Stundenänderung"
+                dense
+                value={stundenGrund}
+                onChange={setStundenGrund}
+                options={STUNDEN_GRUENDE.map((g) => ({ value: g, label: g }))}
+                hint="Steht danach in der Historie neben den Stunden."
+              />
+            )}
             <SelectField
               label="Vertragsart"
               dense