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>

actions/employees.ts

@@ -129,6 +129,8 @@ export async function recordKarenzReturn(payload: {
   return_date: string;
   employment_mode: "unverändert" | "Vollzeit" | "Teilzeit";
   weekly_hours?: number;
+  /** Wiedereingliederungs- oder Elternteilzeit, wenn reduziert zurückgekehrt wird. */
+  reduction_reason?: string;
 }): Promise<ActionResult> {
   return callRpc("record_karenz_return", payload, [`/employees/${payload.employee_id}`, "/employees", "/"]);
 }
@@ -139,6 +141,12 @@ export async function changeEmployeeData(payload: {
   person: Record<string, unknown>;
   contract: Record<string, unknown>;
   role: Record<string, unknown>;
+  /**
+   * Warum sich die Stunden ändern — vertraglich, Bildungs- oder
+   * Pflegeteilzeit. Kein Feld an der Person: es beschreibt *diese*
+   * Änderung und steht deshalb in der Historie, nicht im Stammblatt.
+   */
+  hours_reason?: string;
 }): Promise<ActionResult> {
   return callRpc("change_employee_data", payload, [`/employees/${payload.employee_id}`, "/employees"]);
 }