deploy: move the swarm collector toggle

The one move where the suffix grep is the wrong instrument. There are two
otel options a word apart — `swarm.otel.enable` (one per swarm) and
`otel.enable` (one per hive, every hive runs it) — so `\.otel\.enable`
matches twenty-five references of which most must not change. The module
already carries a comment warning about exactly this, on a line that
names `swarm.otel` in full rather than through a binding.

Triaged by hand and confirmed the other way round: after the move, a grep
for the per-hive option still finds it in the files that should keep it.

Also worth recording what the alias sweep cannot do. `swarm.nix` reads
this as `swarmCfg.otel.enable`, where `swarmCfg = cfg.swarm` and `cfg =
config.services.hyperhive` — an alias bound to an alias, two hops from
the option path. No syntactic sweep resolves that chain, which is why the
module system's own evaluation is the only complete check here and the
static sweeps are a way to narrow the work, not to finish it.

docs/observability.md

@@ -80,7 +80,7 @@ the host is:
 | | runs where | receives from | does |
 |---|---|---|---|
 | **hive tier** — `otel.enable` | every hive with agents | that hive's agents, on the bridge | forwards to the swarm tier. Holds no credential, picks no destination |
-| **swarm tier** — `swarm.otel.enable` | once per swarm | every hive's collector | writes the swarm's store and exports upstream |
+| **swarm tier** — `deploy.otel` | once per swarm | every hive's collector | writes the swarm's store and exports upstream |
 
 An all-local host runs both, and needs nothing said about the hop between them.