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.

components/ui/Pagination.tsx

@@ -0,0 +1,57 @@
+import Link from "next/link";
+
+// Shared by the employee list and the audit log, which both used to render
+// one link per page: 54 of them for ~800 employees, and an unbounded number
+// for the audit log, all in a single overflowing row. This shows the first
+// and last page plus a window around the current one, with the gaps elided.
+const WINDOW = 2;
+
+function pageItems(current: number, total: number): number[] {
+  const pages = new Set<number>([1, total]);
+  for (let p = current - WINDOW; p <= current + WINDOW; p++) {
+    if (p >= 1 && p <= total) pages.add(p);
+  }
+  return [...pages].sort((a, b) => a - b);
+}
+
+type PaginationProps = {
+  page: number;
+  totalPages: number;
+  hrefFor: (page: number) => string;
+  /** Screen-reader name, e.g. "Mitarbeiter:innen" — several lists per app. */
+  label: string;
+};
+
+export function Pagination({ page, totalPages, hrefFor, label }: PaginationProps) {
+  if (totalPages <= 1) return null;
+
+  const current = Math.min(Math.max(1, page), totalPages);
+  const items = pageItems(current, totalPages);
+
+  return (
+    <nav aria-label={`Seiten – ${label}`} className="flex flex-wrap items-center justify-center gap-1 text-sm">
+      {current > 1 && (
+        <Link href={hrefFor(current - 1)} rel="prev" className="rounded px-3 py-1 font-semibold text-ink-body hover:bg-surface">
+          Zurück
+        </Link>
+      )}
+      {items.map((p, i) => (
+        <span key={p} className="flex items-center gap-1">
+          {i > 0 && p - items[i - 1] > 1 && <span className="px-1 text-ink-muted">…</span>}
+          <Link
+            href={hrefFor(p)}
+            aria-current={p === current ? "page" : undefined}
+            className={`rounded px-3 py-1 ${p === current ? "bg-brand-500 font-semibold text-white" : "text-ink-body hover:bg-surface"}`}
+          >
+            {p}
+          </Link>
+        </span>
+      ))}
+      {current < totalPages && (
+        <Link href={hrefFor(current + 1)} rel="next" className="rounded px-3 py-1 font-semibold text-ink-body hover:bg-surface">
+          Weiter
+        </Link>
+      )}
+    </nav>
+  );
+}