deploy: move the controller and swarm-ui toggles

One commit rather than two because they are not independent: the UI's
`enable` had the controller's as its literal default, so moving the
controller alone would leave the UI's default naming an option that no
longer exists.

The UI keeps that derivation in its new home — it is a view onto the
controller's state and reaches it over that daemon's unix socket, so the
host running the controller is the host that can serve it.

Three spellings had to move together for the UI, not one: the `default`,
the `defaultText` shown in the options doc, and the description prose
that names the old path in words. A grep for the option path finds the
first two.

The sweep also reached outside nix: `swarm-controller`'s crate README and
its `//!` module doc both named the option, as did this repo's own
CLAUDE.md and four pages under docs/. An option's name is API, and its
documentation lives wherever someone thought to write it down.

nix/host-modules/swarm.nix

@@ -46,7 +46,7 @@ let
   # `forge.<apex>` is, and no CA in the hierarchy issues for it
   # implicitly. Left out, its vhost falls back to the hive leaf and the
   # swarm's front page opens with a name mismatch.
-  ++ lib.optional swarmCfg.ui.enable swarmCfg.ui.domain
+  ++ lib.optional deployCfg.swarm-ui swarmCfg.ui.domain
   # Every swarm service that claims a gateway name belongs here, and
   # these three were missing it. Membership is what `gateway.lib.tlsFor`
   # consults to pick the services leaf over the hive one, so a name