Phase 1: project foundation for Alpenwerk HR

Scaffolds the Next.js 16 / TypeScript strict / Tailwind v3 app per
NEXTJS_REBUILD_SUPERPROMPT.md, and implements the Foundation slice from
the Phase 1 plan:

- Corrected Supabase schema (supabase/schema.sql): org units, employees,
  history, positions, hire drafts, saved reports, audit log, reorg
  scenarios, role-based profiles, salary-masking view, RLS policies,
  auto-derivation triggers, position-number generator.
- Seed script (supabase/seed.ts): ~800 realistic Austrian employees across
  9 divisions / 16 departments / 35 teams, history, 8 open positions, and
  hr_admin/manager test accounts.
- Supabase clients (lib/supabase/*), design tokens (tailwind.config.ts),
  format/color helpers (lib/format.ts, lib/colors.ts).
- Shared UI kit (components/ui): Avatar, StatusChip, Toast, Modal,
  SlideOver, SegmentedControl, Lookup.
- Auth (login page, Server Actions) and proxy.ts (Next 16's replacement
  for middleware) guarding the authenticated route group.
- Shell (Sidebar, Topbar, NewHireButton stub) and the Dashboard page,
  reading live data via employees_directory.

Employees list/detail, hire wizard, action panels, org chart, positions,
reports, and audit log are deferred to later phases per the plan.

lib/format.ts

@@ -0,0 +1,64 @@
+const dateFormatter = new Intl.DateTimeFormat("de-AT", {
+  day: "2-digit",
+  month: "2-digit",
+  year: "numeric",
+});
+
+const eurFormatter = new Intl.NumberFormat("de-AT", {
+  style: "currency",
+  currency: "EUR",
+});
+
+export function fmtDate(date: string | Date | null | undefined): string {
+  if (!date) return "–";
+  const d = typeof date === "string" ? new Date(date) : date;
+  if (Number.isNaN(d.getTime())) return "–";
+  return dateFormatter.format(d);
+}
+
+export function fmtEUR(amount: number | null | undefined): string {
+  if (amount === null || amount === undefined) return "••• (ausgeblendet)";
+  return eurFormatter.format(amount);
+}
+
+export function initials(firstName: string, lastName: string): string {
+  const a = firstName.trim().charAt(0).toUpperCase();
+  const b = lastName.trim().charAt(0).toUpperCase();
+  return `${a}${b}`;
+}
+
+export function fmtAge(birthDate: string | Date): number {
+  const d = typeof birthDate === "string" ? new Date(birthDate) : birthDate;
+  const today = new Date();
+  let age = today.getFullYear() - d.getFullYear();
+  const hasHadBirthdayThisYear =
+    today.getMonth() > d.getMonth() ||
+    (today.getMonth() === d.getMonth() && today.getDate() >= d.getDate());
+  if (!hasHadBirthdayThisYear) age -= 1;
+  return age;
+}
+
+export function tenure(entryDate: string | Date, endDate?: string | Date | null): string {
+  const start = typeof entryDate === "string" ? new Date(entryDate) : entryDate;
+  const end = endDate ? (typeof endDate === "string" ? new Date(endDate) : endDate) : new Date();
+
+  let years = end.getFullYear() - start.getFullYear();
+  let months = end.getMonth() - start.getMonth();
+  if (end.getDate() < start.getDate()) months -= 1;
+  if (months < 0) {
+    years -= 1;
+    months += 12;
+  }
+  if (years < 0) return "0 Monate";
+
+  const yearPart = years > 0 ? `${years} ${years === 1 ? "Jahr" : "Jahre"}` : "";
+  const monthPart = months > 0 ? `${months} ${months === 1 ? "Monat" : "Monate"}` : "";
+  if (yearPart && monthPart) return `${yearPart}, ${monthPart}`;
+  return yearPart || monthPart || "unter 1 Monat";
+}
+
+export function daysBetween(a: string | Date, b: string | Date = new Date()): number {
+  const start = typeof a === "string" ? new Date(a) : a;
+  const end = typeof b === "string" ? new Date(b) : b;
+  return Math.round((end.getTime() - start.getTime()) / (1000 * 60 * 60 * 24));
+}