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.

docs/swarm/services.md

@@ -5,12 +5,12 @@ matrix homeserver, the SSO provider, the CA. Two options say where the
 optional ones live, and everything else derives:
 
 ```nix
-services.hyperhive.enableAllLocalDefaults = true;   # everything on this box
+services.hyperhive.deploy.singleHostSwarm = true;   # everything on this box
 # or, for a dedicated services host with hives elsewhere:
 services.hyperhive.deploy.allSwarmServices = true;
 ```
 
-`enableAllLocalDefaults` is the all-on-one-box switch: it defaults both
+`singleHostSwarm` is the all-on-one-box switch: it defaults both
 `deploy.allSwarmServices` (the shared services run here) and
 `swarm.ca.autoConfigure` (the swarm CA is generated here). Each derived
 toggle can still be set on its own, so "all local except X" needs no
@@ -33,7 +33,7 @@ Those two options are what makes the difference between deployments, so
 the shapes worth naming are the ones they produce:
 
 - **All-local.** Everything on one machine:
-  `enableAllLocalDefaults = true`. Setup is automatic apart from
+  `singleHostSwarm = true`. Setup is automatic apart from
   choosing a domain and creating the first user.
 - **Services on the swarm controller host.**
   `deploy.allSwarmServices = true` there; the required services