swarm: say "no queue coordinates", never "a hive with no queue"

The swarm always has exactly one queue; a hive can only lack its
address. Reworded every prose site this PR added that stated or
implied the opposite, to name what is actually absent (coordinates,
credential, or address) instead of the queue itself.

Refs #3805

docs/swarm/README.md

@@ -385,9 +385,9 @@ above, plus `HIVE_AGENT_OIDC_CLIENT_SECRET_FILE` and
 `HIVE_AGENT_OIDC_CLIENT_ID_FILE`, which point into the unit's own credentials
 directory. The last two come from the delivered credential rather than from
 config — see [`secrets.md`](secrets.md#hive-level--one-of-each-per-hive) for
-how it gets there. A hive with no queue sets none of the four and each agent
-logs that it has none; a half-set environment logs an error and the harness
-keeps serving.
+how it gets there. A hive that hasn't been given the queue's address for its
+agents sets none of the four and each agent logs that it has none; a half-set
+environment logs an error and the harness keeps serving.
 
 ### Swarm-wide forge webhooks
 

docs/swarm/secrets.md

@@ -180,7 +180,7 @@ reads them out of its own `$CREDENTIALS_DIRECTORY`, owned by the agent user
 and by nobody else. `hive-c0re` never reads the bytes at any point: it runs as
 `hive-core`, which is the reason a copy wasn't an option either. When the
 files aren't there the daemon forwards nothing and says so in its journal, and
-the harness logs that it has no queue — the same absent-and-legal state, twice,
+the harness logs that it has no queue coordinates — the same absent-and-legal state, twice,
 rather than a container that refuses to start.
 
 ⚠️ **Service↔store mTLS is its own trust domain.** A credential you must