deploy: rename enableAllLocalDefaults to deploy.singleHostSwarm

Same defect as the switch below it, one tier up: it sat at the TOP of
`services.hyperhive`, a namespace that is meant to be everything about
hyperhive rather than the settings of a single hive. Whether this box is
the whole deployment is as per-host as a decision gets.

The name follows mara's sentence for what it means — "everything in the
swarm is running on this host" — rather than naming its mechanism.
"Defaults" was doing no work: it is not a defaults toggle, it is a claim
about where the swarm lives, and the pair now reads as the containment it
already was, singleHostSwarm implying allSwarmServices plus this hive.

One site was a setter rather than a reference: module-eval's `allLocal`
fixture passes an attrset merged into `services.hyperhive`, so its key
carries the path and had to become `deploy.singleHostSwarm`. A rename by
bare identifier is right for the twelve prose mentions and wrong for
exactly this one, which is worth knowing before the next rename.

nix/host-modules/swarm-ca.nix

@@ -11,7 +11,7 @@
 # Two provisioning modes, ONE structure — what differs is who puts the
 # artifacts on disk, never what the artifacts are:
 #
-#   - autoconfigured (`services.hyperhive.enableAllLocalDefaults`, or
+#   - autoconfigured (`services.hyperhive.deploy.singleHostSwarm`, or
 #     `autoConfigure` set directly): the unit below generates the root
 #     here on first boot.
 #   - operator-provided (multi-host): the operator installs the root cert
@@ -68,7 +68,7 @@ in
         Run the whole swarm CA on this one host: generate the swarm
         root when it is missing, and issue this hive's CA under it.
 
-        `services.hyperhive.enableAllLocalDefaults` turns this on as
+        `services.hyperhive.deploy.singleHostSwarm` turns this on as
         part of the all-on-one-box mode. Set it here directly to run the
         CA on a host that is not otherwise all-local.