deploy: move the matrix homeserver toggle out of swarm

swarm.matrix.enable was the last toggle still spelled swarm.*, which
is the namespace every host in the swarm agrees on - and "does this
host run the homeserver" is exactly what differs between them. It
moves to deploy.matrix.enable with the rest; the genuinely swarm-wide
matrix settings stay where they are.

mkRenamedOptionModule keeps existing configs evaluating with one
warning naming both paths.

The sweep for readers had to be unanchored and cross-language: three
of them were outside nix, including a hive-c0re error message telling
the operator to set the old name. A dotted grep also cannot see the
rename module's own list form, so that was checked separately.

nix/host-modules/swarm-required-services.nix

@@ -48,15 +48,11 @@ in
 
   # Same precedence reasoning as ./local-defaults.nix: fills in for an
   # operator who hasn't spoken, yields to one who has.
-  config.services.hyperhive.swarm = {
-    # The last one still spelled `swarm.*.enable`. Everything else that
-    # used to derive here — the queue, the SSO provider, the collector,
-    # the metrics pair, the log store — now derives below under
-    # `deploy.*`, because "does THIS host run it" is a per-host decision
-    # and `swarm.*` has to be identical on every host. Same switch, same
-    # rule, different attribute path.
-    matrix.enable = lib.mkDefault swarmCfg.enableRequiredServices;
-  };
+  #
+  # Everything derives under `deploy.*` now, because "does THIS host run
+  # it" is a per-host decision and `swarm.*` has to be identical on every
+  # host. Same switch, same rule, one attribute path.
+  config.services.hyperhive.deploy.matrix.enable = lib.mkDefault swarmCfg.enableRequiredServices;
 
   # The collector that feeds the pair above (note: no `swarm.` prefix,
   # this is ./otel.nix's existing per-hive option).