hive-c0re's container-resource exporter already targets this hive's own
collector (environment.nix derives the bridge address), so the upstream
header it was loaded with has nowhere to be presented: that hop is
unauthenticated for every producer on the host, and the credential
belongs to the swarm tier, which is the one that leaves the swarm.
Drop the LoadCredential entry and the auth_headers() reader with it.
The option itself stays -- swarm-otel.nix is its real consumer, via
EnvironmentFile on the collector unit.
Also corrects three descriptions that this makes false, or that were
already false: the module doc claimed to reuse the config "Claude Code's
in-container SDK export uses", which stopped being true when agents
moved off that path; the nix comment claimed the secret is "the same one
the agent containers get, forwarded via nspawn --load-credential", which
lost its last producer earlier; and docs/observability.md described an
Authorization header on a hop that will no longer send one. The
headersCredential option's own docs already said it reaches "neither an
agent container nor a hive's own collector" -- this makes that true
rather than aspirational.