feat(swarm-controller): new crate, a unix-socket listener and nothing else

First half of the swarm-controller slice: the crate, its workspace entry
and its daemonBins entry, so the systemd unit that follows has a binary
to point at.

It serves one health endpoint and owns no state. That is the whole
intent -- this makes the unit real (service user, runtime and state
directories, socket, nginx reachability) so the swarm-level surfaces
that follow have somewhere to land. Inventing those surfaces now would
bake in a shape nobody has agreed to.

The socket gets its own runtime directory rather than sharing
hive-c0re's. nginx reaches a unix upstream by having the socket's
directory bind-mounted into the gateway container, so co-locating this
socket with the host admin socket would hand the gateway that socket
too.

Cargo.lock

@@ -4421,6 +4421,17 @@ version = "2.6.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "13c2bddecc57b384dee18652358fb23172facb8a2c51ccc10d74c157bdea3292"
 
+[[package]]
+name = "swarm-controller"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "axum",
+ "tokio",
+ "tracing",
+ "tracing-subscriber",
+]
+
 [[package]]
 name = "syn"
 version = "1.0.109"