Add customergroup bulk reorder and list editable flag.

Expose PUT /customergroup/order for exact-set sort updates, keep create/update name-only, and mark POS/Lieferanten as non-editable in list responses.

docs/api/routes/customergroup/list.md

@@ -4,7 +4,10 @@ Protected. Requires a valid session cookie (`credentials: 'include'`).
 
 List customer groups
 
-Lists customer groups for the authenticated user's selected company.
+Lists customer groups for the selected company, ordered by `sort`.
+Each item includes `editable`: `false` for implicit `POS` / `Lieferanten`
+(name locked), `true` otherwise. Reorder via `PUT /customergroup/order`.
+
 
 ## Response `200`
 
@@ -15,7 +18,9 @@ Customer group list
   "customergroups": [
     {
       "id": 1,
-      "name": "…"
+      "name": "…",
+      "sort": 1,
+      "editable": true
     }
   ]
 }