feat: 导出Excel多sheet，按标签分页

- 文件名：精油配方YYYY-MM-DD.xlsx
- 第一个sheet"全部"包含所有配方
- 每个标签一个单独的sheet
- 使用SheetJS生成真正的xlsx格式

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -18,7 +18,8 @@
     "html2canvas": "^1.4.1",
     "pinia": "^2.3.1",
     "vue": "^3.5.32",
-    "vue-router": "^4.6.4"
+    "vue-router": "^4.6.4",
+    "xlsx": "^0.18.5"
   },
   "devDependencies": {
     "@vitejs/plugin-vue": "^6.0.5",