Declare every module's data; the backup holder measures it (hq ADR 0233)

Backup lines are derived from each module's data section instead of written by hand; the holder
measures declared items, reads the array under them, and deletes a retired item only after a last
restore point; the Go providers say each held consumer's size so an empty replacement is seen.

modules/nextcloud/module.json

@@ -44,6 +44,16 @@
       "why": "files and sync, over http; a public name is a route grant later"
     }
   ],
+  "data": {
+    "own": [
+      {
+        "id": "html",
+        "path": "${dir:html}",
+        "class": "valuable",
+        "why": "the instance's configuration, its secret and installed apps; the files are in the object store"
+      }
+    ]
+  },
   "resources": [
     {
       "id": "mesh-state",
@@ -117,12 +127,5 @@
         }
       }
     ]
-  },
-  "contributions": [
-    {
-      "seat": "node-backup",
-      "kind": "backup",
-      "content": "path ${dir:html}\n"
-    }
-  ]
+  }
 }