Let a rehire choose the position, and make it work at all

Clicking "Wiedereinstellen" could never succeed. rehire_employee has always
demanded a position and refuses without one, but the panel offered only a
date and sent only a date — so every rehire ended on an error the dialog
gave no way to fix.

The panel now picks from the open positions, the same list and layout the
transfer panel uses, and warns before submitting when the date falls outside
the chosen position's validity. The old position is deliberately not a
silent default: it may since have been filled, ended, or gone.

Behind that sat a second fault, hidden by the first: the status assignment

    status = case when v_date <= current_date then 'Aktiv' else 'Geplant' end

is text, and the column is employment_status. Postgres refuses that outright,
so the function would have failed even with a position. It surfaced only once
the earlier check stopped firing — the same pattern as hire_employee this
morning, where three faults sat in a queue.

rehire_employee also placed people without checking anything. It now applies
the rule from 20260810100000: the date must lie in the position's validity,
and no assignment may still stand. A rehire could otherwise land on an
occupied position and be caught by the partial index, with a message that
explains nothing.

My first verification of the cast was wrong and passed a broken state:
plpgsql converts silently when assigning to a variable, so the probe proved
nothing. Redone as an UPDATE against a column, which is the case that fails.

Verified end to end against the live database, rolled back: Stefan Egger
returns as Aktiv on a free position, with the assignment and the
Wiedereintritt entry. Without a position, on an occupied one, and on one not
yet valid, it is refused — each with its own message.

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

actions/employees.ts

@@ -129,7 +129,19 @@ export async function changeEmployeeData(payload: {
   return callRpc("change_employee_data", payload, [`/employees/${payload.employee_id}`, "/employees"]);
 }
 
-export async function rehireEmployee(payload: { employee_id: string; rehire_date: string }): Promise<ActionResult> {
+/**
+ * `position_id` ist Pflicht — die Datenbankfunktion verlangt sie seit jeher.
+ *
+ * Die alte Stelle taugt nicht als stille Vorgabe: sie kann inzwischen besetzt
+ * oder ausgelaufen sein. Sie fehlte hier nur in der Signatur, weshalb jede
+ * Wiedereinstellung an einer Meldung scheiterte, die im Dialog nicht zu
+ * beheben war.
+ */
+export async function rehireEmployee(payload: {
+  employee_id: string;
+  rehire_date: string;
+  position_id: string;
+}): Promise<ActionResult> {
   return callRpc("rehire_employee", payload, [`/employees/${payload.employee_id}`, "/employees", "/"]);
 }