deploy: name the swarm collector swarm-otel, not otel

Per review: `deploy.otel` does not imply swarm level, and there is a
hive-tier collector too -- `services.hyperhive.otel.enable`, which every
hive runs. The tier is the entire distinction between the two, so the
name has to carry it, matching `deploy.swarm-controller` and
`deploy.swarm-ui`.

15 swarm-tier references renamed across 8 files. The hive-tier
collector's 16 references are deliberately untouched, verified as a
control on the same command.

Three spellings needed three different patterns, all inside this one
rename: the dotted path; the `mkRenamedOptionModule` target written as a
nix LIST (`[ ... "deploy" "otel" "enable" ]`), which no dotted grep can
match; and prose in docs/observability.md spelled `deploy.otel` with
neither `.enable` nor a leading dot. Unanchored `deploy\.otel\b` is the
only pattern that finds all three.

nix/host-modules/otel.nix

@@ -61,7 +61,7 @@ in
       their own containers can reach.
 
       That collector forwards to the swarm's
-      ({option}`services.hyperhive.deploy.otel.enable`), which holds the
+      ({option}`services.hyperhive.deploy.swarm-otel.enable`), which holds the
       upstream credential and writes the swarm's store. So an agent never
       sees the credential, and neither does this tier.
 
@@ -81,7 +81,7 @@ in
         has left the swarm.
 
         Read by the swarm's collector
-        ({option}`services.hyperhive.deploy.otel.enable`), which is the only
+        ({option}`services.hyperhive.deploy.swarm-otel.enable`), which is the only
         tier that holds the upstream credential. An agent is handed the
         *first* hop instead — this hive's own collector — so this value is
         never given to a container.