feat: add article search index endpoint and category export.zip

- Add GET /api/articleIndex returning the article search index (listSearchIndex)
- Add GET /api/category/export.zip returning a kategorien.zip with a
  Windows-1252 CSV (depth-first, Ebene N columns) plus one AVIF per category image
  (content-addressed, deduplicated) using jszip

package.json

@@ -24,6 +24,7 @@
     "ink": "^7.1.0",
     "ink-text-input": "^6.0.0",
     "jsonwebtoken": "^9.0.3",
+    "jszip": "^3.10.1",
     "libdashstore": "file:../dashdbschema",
     "mssql": "^12.6.0",
     "react": "^19.2.7",