fix(docs): add donut _category_.json to fix broken /category/donut link

Author: Aldiwildan77

docs/donut/_category_.json

@@ -0,0 +1,8 @@
+{
+  "label": "Donut",
+  "position": 6,
+  "link": {
+    "type": "generated-index",
+    "description": "Donut is Mocha's community matchmaking feature — automatically pairs members for 1-on-1 or small-group interactions."
+  }
+}