Let the employee list be sorted A-Z or Z-A

Sorting lives in the URL, not the browser. The list is built on the
server and fetched a page at a time, so a client-side sort would only
reorder the fifteen rows on screen — with 867 people that promises an
alphabetical list and delivers something else on page 2.

The sort key is the surname, because that is how the column reads:
"Aigner, Manuel", and whoever looks for someone looks under A. Postgres
runs with the Austrian collation, so Ö sorts with O rather than at the
end of the alphabet.

Only the surname reverses. The id stays ascending: it decides nothing
except ties, and it exists to keep the order total across page
boundaries. Reversing it too would still be deterministic but would flip
the fourteen Winklers relative to each other for no reason anyone asked
for.

The select sits in the filter bar rather than in a clickable column
header — a header would suggest it sorts what is on screen.

Verified: compiled SQL is `order by last_name desc, id` for Z-A; the
parse and direction rules are covered by tests that were mutation-checked
(breaking each rule turns them red). Not verified in the browser — the
login goes through the company account, and the Supabase instance no
longer resolves.

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

components/employees/EmployeeFilters.tsx

@@ -4,6 +4,7 @@ import { usePathname, useRouter, useSearchParams } from "next/navigation";
 import { useEffect, useState } from "react";
 import { FILTER_SELECT_CLASS } from "@/components/ui/Field";
 import { SearchInput } from "@/components/ui/SearchInput";
+import { SORTIERUNGEN, STANDARD_SORTIERUNG } from "@/lib/employee-sort";
 
 type EmployeeFiltersProps = {
   /** Der ganze Baum, in Tiefensuche-Reihenfolge. */
@@ -104,6 +105,23 @@ export function EmployeeFilters({ units, depthOf, locations }: EmployeeFiltersPr
           </option>
         ))}
       </select>
+      {/* Die Sortierung steht bewusst neben den Filtern und nicht in der
+          Tabellenüberschrift: sortiert wird über den ganzen Bestand, nicht
+          über die fünfzehn Zeilen dieser Seite. Ein anklickbarer Spaltenkopf
+          verspräche das Gegenteil. Anders als die Filter hat sie keinen
+          leeren Eintrag — irgendeine Reihenfolge hat die Liste immer. */}
+      <select
+        aria-label="Liste sortieren"
+        defaultValue={searchParams.get("sort") ?? STANDARD_SORTIERUNG}
+        onChange={(e) => updateParam("sort", e.target.value)}
+        className={FILTER_SELECT_CLASS}
+      >
+        {SORTIERUNGEN.map((s) => (
+          <option key={s.value} value={s.value}>
+            {s.label}
+          </option>
+        ))}
+      </select>
       {/* Der Dienstwagen stand hier einmal als eigenes Auswahlfeld. Er ist
           jetzt eines von rund zwanzig Kriterien unter Berichte, zusammen mit
           Vertragsart, Kollektivvertrag, Eintrittszeitraum und dem Rest —