homepage: add Marreta as a user-category service

Adds the Marreta content-reader tile (http://marreta.franksdank.cloud,
probe 127.0.0.1:8082 via gluetun's publish) to the user grid so regular
authenticated users get a link to it. Registry-driven e2e picks it up
automatically.

shared/homepage/services.json

@@ -98,6 +98,17 @@
     "wip": false,
     "showLink": true
   },
+  {
+    "name": "Marreta",
+    "category": "user",
+    "description": "Clean, ad-free article reader. Paste any URL, get just the article.",
+    "url": "http://marreta.franksdank.cloud",
+    "docs": "",
+    "probe": "127.0.0.1:8082",
+    "method": "http",
+    "wip": false,
+    "showLink": true
+  },
   {
     "name": "Sonarr",
     "category": "admin",