Phase 2/3: Employees list/detail + mutation RPCs + action panels

- supabase/functions.sql, functions_2.sql: Postgres RPCs for every
  employee/position/reorg mutation (hire, terminate, transfer, promote,
  start/adjust/return karenz, change data, rehire, create position, staff
  internally, apply/undo reorg). Each resolves manager_id server-side,
  writes history + audit atomically, and enforces hr_admin via
  require_hr_admin() (backed by the existing RLS policy).
- actions/employees.ts, positions.ts, reorg.ts: Server Actions wrapping
  the RPCs, returning success/error for client-side toast handling.
- Employees list (search/filter/pagination) and detail (4 tabs: Stammdaten,
  Vertrag & Gehalt, Organisation, Historie) reading from employees_directory.
- 6 action slide-over panels: Transfer, Promote, Karenz (start/adjust/
  return), Daten aendern (person+contract diffing), Terminate (with direct-
  report reparenting warning + offboarding checklist), Rehire.
- lib/org.ts: shared division/department/team/location lookups.

Verified live: promote mutation updates salary, writes history/audit, and
the detail page reflects it after refresh, no console errors.

Note: the spec's Karenz-verwalten panel only covers employees already on
Karenz; added a start-Karenz mode (Karenzbeginn/geplante Rueckkehr) to
cover the Aktiv-employee case implied by the header button but not
specified in the panel list.

components/employees/tabs/StammdatenTab.tsx

@@ -0,0 +1,28 @@
+import { fmtAge, fmtDate } from "@/lib/format";
+import type { Database } from "@/lib/supabase/types";
+
+type EmployeeRow = Database["public"]["Views"]["employees_directory"]["Row"];
+type Location = Database["public"]["Tables"]["locations"]["Row"];
+
+export function StammdatenTab({ employee, location }: { employee: EmployeeRow; location?: Location }) {
+  const rows: [string, string][] = [
+    ["Geburtsdatum", `${fmtDate(employee.birth_date)} (${fmtAge(employee.birth_date)} Jahre)`],
+    ["SV-Nummer", employee.sv_nummer ?? "–"],
+    ["Staatsbürgerschaft", employee.nationality],
+    ["E-Mail", employee.email],
+    ["Telefon", employee.phone ?? "–"],
+    ["Standort", location ? `${location.name} (${location.country})` : "–"],
+    ["Adresse", employee.address ?? "–"],
+    ["Geschlecht", employee.gender === "m" ? "männlich" : "weiblich"],
+  ];
+  return (
+    <dl className="grid grid-cols-1 gap-x-8 gap-y-4 sm:grid-cols-2 lg:grid-cols-3">
+      {rows.map(([label, value]) => (
+        <div key={label}>
+          <dt className="text-xs font-semibold uppercase tracking-wide text-ink-muted">{label}</dt>
+          <dd className="mt-1 text-sm text-ink">{value}</dd>
+        </div>
+      ))}
+    </dl>
+  );
+}