feat(frontend): Tauri Apps, Shared UI Library und Nix Flake

- packages/ui: Shared React Component Library (Button, Card, Badge, Input)
  mit Tailwind v4 @theme Design Tokens (oklch)
- apps/web: ERP Web-UI (Vite + React + Tailwind v4, API-Proxy :8080)
- apps/scanner: Tauri v2 Mobile App mit Barcode-Scanner Plugin
  (cfg(mobile) für Desktop-Kompatibilität)
- flake.nix: Nix Flake mit rust-overlay, Tauri System-Deps (GTK,
  WebKitGTK, libsoup, OpenSSL), ersetzt shell.nix
- justfile: Dev-Befehle für alle Projekte (backend, cli, web, scanner)
- frontend/CLAUDE.md: Agent Guide mit Base UI Docs Referenz

frontend/apps/scanner/vite.config.ts

@@ -0,0 +1,22 @@
+import { defineConfig } from 'vite';
+import react from '@vitejs/plugin-react';
+import tailwindcss from '@tailwindcss/vite';
+
+const host = process.env.TAURI_DEV_HOST;
+
+export default defineConfig({
+  plugins: [tailwindcss(), react()],
+  clearScreen: false,
+  server: {
+    port: 1420,
+    strictPort: true,
+    host: host || false,
+    hmr: host
+      ? {
+          protocol: 'ws',
+          host,
+          port: 1421,
+        }
+      : undefined,
+  },
+});