module-eval: three duplicate nixosSystem fixtures come from shared.nix

builder.nix's bare, servicesHere and natsHere were exact copies of
shared.bareWithController, swarm-services-switch's swarmServicesHere and
nats-authelia's natsOldPath. The last two move into shared.nix; each file
rebinds them under its local name, so no case changes.

nix/module-eval/builder.nix

@@ -7,6 +7,7 @@
   lib,
   self,
   nixosSystem,
+  shared,
 }:
 let
   inherit
@@ -19,11 +20,10 @@ let
         ;
     })
     hive
-    hiveWithController
     runGroup
     ;
 
-  bare = hiveWithController { };
+  bare = shared.bareWithController;
 
   # On the store's host, which mints the builder's store identity.
   withBuilder = hive {
@@ -31,16 +31,13 @@ let
     deploy.builder.enable = true;
   };
 
-  servicesHere = hiveWithController { deploy.allSwarmServices = true; };
+  servicesHere = shared.swarmServicesWithController;
   # Short-circuits on `assertion`, so only a failing one has its message read.
   refusedWithoutIdentity =
     m:
     lib.any (a: !a.assertion && lib.hasInfix "deploy.builder.enable requires" a.message) m.assertions;
 
-  natsHere = hive {
-    swarm.nats.enable = true;
-    swarm.nats.authPackage = pkgs.emptyDirectory;
-  };
+  natsHere = shared.natsOldPath;
 
   autheliaHere = hive {
     deploy.bao.enable = true;