manatee: Add schema

The household weekly plan at schema.ppp.pm: its module, certificate,
DNS record, backup and secrets. The link to puppy-tracker is prepared
but commented out until puppy-tracker with the integration feed is
deployed.

hosts/manatee/modules/default.nix

@@ -29,6 +29,7 @@ in
       puppy-tracker.enable = true;
       solo-referee.enable = true;
       todo.enable = true;
+      schema.enable = true;
     };
   };
 }