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

docs/api/routes/posterminal/setOn.md

@@ -0,0 +1,38 @@
+# `PUT /posterminal/{id}/category/{categoryId}`
+
+Protected. Requires a valid session cookie (`credentials: 'include'`).
+
+Enable category on terminal
+
+Toggles a single category's visibility on a terminal (idempotent).
+
+## Path parameters
+
+| Param | Required | Type | Description |
+|-------|----------|------|-------------|
+| `id` | yes | integer |  |
+| `categoryId` | yes | integer |  |
+
+## Response `200`
+
+Updated category IDs for this terminal
+
+```json
+{
+  "id": 1,
+  "categoryIds": []
+}
+```
+
+## Errors
+
+| Status | Description |
+|--------|-------------|
+| 400 | No company selected or invalid terminal/category — `{"error":"…"}` |
+| 401 | Unauthorized — `{"error":"…"}` |
+| 403 | Not authorized — `{"error":"…"}` |
+| 404 | Posterminal not found — `{"error":"…"}` |
+
+---
+
+_Generated from `@openapi` JSDoc. Do not edit by hand — run `npm run docs:api`._