feat: initial workflow portal - multi-tenant architecture

- Backend: Node.js + Express + TypeScript + Prisma + PostgreSQL
- Frontend: React + TypeScript + Tailwind CSS + Vite
- Multi-tenant with role-based access (SystemAdmin, Technician, Customer)
- Workflow editor with drag-and-drop steps
- JWT authentication with refresh tokens
- German UI throughout

frontend/index.html

@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html lang="de">
+  <head>
+    <meta charset="UTF-8" />
+    <link rel="icon" type="image/svg+xml" href="/vite.svg" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Workflow Portal</title>
+  </head>
+  <body class="bg-gray-50 text-gray-900 antialiased">
+    <div id="root"></div>
+    <script type="module" src="/src/main.tsx"></script>
+  </body>
+</html>