Org assignment history, mobile support, and a correctness pass

Data model
- employee_assignments records org placement over time (valid_from/valid_to),
  written by a trigger on `employees` rather than inside each RPC: ~70
  `update employees` statements spread over fifteen migrations mean per-call
  bookkeeping would miss paths today and again with every future RPC. A
  partial unique index enforces the one-open-interval invariant the trigger
  relies on when closing the current row.
- The Organigramm gains a Stichtag (default today). Membership comes from
  entry/exit/karenz, past placement from the new history, future placement
  projected from pending_org_changes. Placements predating the migration are
  backfilled with today's values and flagged as such in the UI, since
  employee_history only ever stored free text and cannot be reconstructed.

Correctness
- Reports and exports silently truncated at PostgREST's 1000-row cap
  (db.max_rows); employee_history is already past it at ~800 staff. Every
  whole-table read now pages explicitly.
- XLSX date cells were a day early: ExcelJS converts a Date to an Excel
  serial straight off getTime(), so a Date built at local midnight lands on
  the previous day's serial in any positive-offset zone.
- Date handling is pinned to Europe/Vienna throughout, and date-only strings
  are formatted without a Date round-trip. The dashboard's YTD window was
  built by round-tripping a local Date through toISOString(), which shifted
  it a day early and dropped 31 December entirely.
- Export routes parsed measure/group/split/eventType with unchecked `as`
  casts, so an unknown value reached column headers as `undefined` and the
  Content-Disposition filename. Parsed against the label maps now, with the
  filename slugged as a backstop.
- toXlsx keyed columns by header text, silently dropping the second of any
  two columns sharing a name — split columns take their header from data.
- The org chart tree walks had no cycle guard; nothing in the schema forbids
  a manager_id cycle, and one would hang the tab rather than misreport.
- The login page reflected ?error= verbatim, letting anyone put arbitrary
  text on the real sign-in screen; messages are looked up by code now.
- React Flow needs elementsSelectable on, or it sets pointer-events:none on
  the whole node and the expand control stops responding.

UI
- Mobile: the shell was unusable below lg — a fixed 236px margin pushed
  content off-screen with no mobile navigation at all. The sidebar is now a
  drawer, dvh replaces vh, safe-area insets are honoured, inputs are 16px so
  iOS stops zooming on focus, and form grids stack.
- Org chart nodes redesigned: per-kind accent stripes and icons, vacant
  roles called out, expand control moved to the bottom edge carrying the
  child count.
- Pagination is windowed; it previously rendered one link per page (54 for
  the employee list, unbounded for the audit log).
- Positions page reduced to open positions with a single "Besetzen" action.
- The employee Organisation tab links into the org chart focused on that
  person, reusing the chart's existing search-match highlighting.

Also included, uncommitted until now
- Dependants, HR notes, academic titles, split address fields, position
  validity and role/employment fields, with their migrations and UI.
- Docker/compose deployment setup, data-model and security-review docs.

app/(app)/employees/page.tsx

@@ -2,6 +2,7 @@ import Link from "next/link";
 import { Suspense } from "react";
 import { EmployeeFilters } from "@/components/employees/EmployeeFilters";
 import { Avatar } from "@/components/ui/Avatar";
+import { Pagination } from "@/components/ui/Pagination";
 import { StatusChip } from "@/components/ui/StatusChip";
 import { fmtDate } from "@/lib/format";
 import { breadcrumbFor, loadOrgMaps } from "@/lib/org";
@@ -126,19 +127,7 @@ export default async function EmployeesPage({ searchParams }: EmployeesPageProps
         </table>
       </div>
 
-      {totalPages > 1 && (
-        <div className="flex items-center justify-center gap-2 text-sm">
-          {Array.from({ length: totalPages }, (_, i) => i + 1).map((p) => (
-            <Link
-              key={p}
-              href={pageHref(params, p)}
-              className={`rounded px-3 py-1 ${p === page ? "bg-brand-500 text-white" : "text-ink-body hover:bg-surface"}`}
-            >
-              {p}
-            </Link>
-          ))}
-        </div>
-      )}
+      <Pagination page={page} totalPages={totalPages} hrefFor={(p) => pageHref(params, p)} label="Mitarbeiter:innen" />
     </div>
   );
 }