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.

components/ui/Toast.tsx

@@ -0,0 +1,48 @@
+"use client";
+
+import { createContext, useCallback, useContext, useState, type ReactNode } from "react";
+
+type ToastVariant = "success" | "error" | "info";
+type ToastItem = { id: number; message: string; variant: ToastVariant };
+type ToastContextValue = { showToast: (message: string, variant?: ToastVariant) => void };
+
+const ToastContext = createContext<ToastContextValue | null>(null);
+
+const VARIANT_STYLES: Record<ToastVariant, string> = {
+  success: "bg-success-text",
+  error: "bg-danger-solid",
+  info: "bg-info-text",
+};
+
+export function ToastProvider({ children }: { children: ReactNode }) {
+  const [toasts, setToasts] = useState<ToastItem[]>([]);
+
+  const showToast = useCallback((message: string, variant: ToastVariant = "success") => {
+    const id = Date.now() + Math.random();
+    setToasts((prev) => [...prev, { id, message, variant }]);
+    setTimeout(() => setToasts((prev) => prev.filter((t) => t.id !== id)), 4000);
+  }, []);
+
+  return (
+    <ToastContext.Provider value={{ showToast }}>
+      {children}
+      <div className="pointer-events-none fixed bottom-4 right-4 z-[100] flex flex-col gap-2">
+        {toasts.map((t) => (
+          <div
+            key={t.id}
+            role="status"
+            className={`pointer-events-auto rounded px-4 py-2 text-sm font-semibold text-white shadow-lg ${VARIANT_STYLES[t.variant]}`}
+          >
+            {t.message}
+          </div>
+        ))}
+      </div>
+    </ToastContext.Provider>
+  );
+}
+
+export function useToast(): ToastContextValue {
+  const ctx = useContext(ToastContext);
+  if (!ctx) throw new Error("useToast must be used within a ToastProvider");
+  return ctx;
+}