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/src-tauri/tauri.conf.json

@@ -0,0 +1,37 @@
+{
+  "$schema": "https://raw.githubusercontent.com/nicfit/tauri/tauri-v2/crates/tauri-cli/schema.json",
+  "productName": "Effigenix Scanner",
+  "version": "0.1.0",
+  "identifier": "de.effigenix.scanner",
+  "build": {
+    "frontendDist": "../dist",
+    "devUrl": "http://localhost:1420",
+    "beforeDevCommand": "pnpm dev",
+    "beforeBuildCommand": "pnpm build"
+  },
+  "app": {
+    "withGlobalTauri": false,
+    "windows": [
+      {
+        "title": "Effigenix Scanner",
+        "width": 400,
+        "height": 700,
+        "resizable": true
+      }
+    ],
+    "security": {
+      "csp": null
+    }
+  },
+  "bundle": {
+    "active": true,
+    "targets": "all",
+    "icon": [
+      "icons/32x32.png",
+      "icons/128x128.png",
+      "icons/128x128@2x.png",
+      "icons/icon.icns",
+      "icons/icon.ico"
+    ]
+  }
+}