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/swarm-nats.nix

@@ -536,7 +536,7 @@ in
     # and only this one reads `scrapeTargets`. Written in full so the gate
     # and the option it gates are visibly the same path.
     services.hyperhive.swarm.otel.scrapeTargets =
-      lib.mkIf config.services.hyperhive.deploy.otel.enable
+      lib.mkIf config.services.hyperhive.deploy.swarm-otel.enable
         {
           nats = "127.0.0.1:${toString cfg.metricsPort}";
         };