The option defaulted to pkgs.swarm-ui, which does not exist: this
project has no overlay - flake.nix's nixosModules.default wires package
options with mkDefault from its own package set, and swarm.controller
does exactly that. The default would have failed to evaluate on any real
deployment, not just in a test harness.
Found by the gate forcing .package: the earlier probes passed because
they only read option values that never touched it.
New swarm-ui module: enable (derived from swarm.controller.enable - the
UI reads that daemon's state over its socket, so the host that runs the
controller is the host that can serve the UI), domain (defaults to the
swarm apex; an option so a hive can pin it like forge/matrix can), and
package.
Adds the name to swarm.serviceDomains, which is both the services
sub-CA's nameConstraints set and the leaf's SAN set. The apex is a
SIBLING of forge./chat./auth., not a parent, so nothing issues for it
implicitly - left out, the vhost falls back to the hive leaf and the
swarm's front page opens with a name mismatch.
Asserts the UI domain differs from the hive domain: the gateway's
default server already answers for the latter, and two vhosts claiming
one server_name resolve to whichever nginx picks rather than erroring.
