swarm: refuse hive names that CONTAIN a word identifiers are composed from

Hive-scoped identifiers are built by joining a hive name with fixed words —
`hive-<name>`, `hive-<name>-agent` — so a hive called `foo-agent` produces
exactly the id hive `foo`'s agent containers produce. The queue's responder
resolves it as the agents, and that hive silently receives an agent grant
instead of its own; a NATS denial reaches a client as a timeout, so nothing
names the cause. Equality cannot see this: the two NAMES differ, only the
composed strings collide.

Deliberately a second file rather than three more entries in
`reserved-names.nix`. That list is matched by equality against a whole name and
every entry is a value some component emits; applying containment to it would
refuse `forgeworks` and `operator-hq` for failures that do not exist. The two
lists differ in subject (hive-only vs both), matcher (substring vs equality)
and admission rule, and each file's header says so.

No Rust change: `HIVE_RESERVED_NAMES` answers "may an AGENT be called this",
which stays an equality question — an agent name is never composed into these
identifiers.

Measured against the predicate rather than assumed:

  pr1ma=ok alpha=ok forgeworks=ok operator-hq=ok
  foo-agent=REFUSED beehive=REFUSED swarm=REFUSED myswarmx=REFUSED

The four `ok` cases are the control: `forgeworks` and `operator-hq` are exactly
what a merged list would have refused.

nix/reserved-names.nix

@@ -25,6 +25,9 @@
 # `from`/`to`, or a component name the collector builds pipelines from — not a
 # word that merely looked risky. A name in here that nothing emits is a refusal
 # with no failure behind it.
+#
+# ⚠️ Matched by EQUALITY. Words forbidden *inside* a hive name live in
+# `./reserved-hive-fragments.nix` — read its header before merging the two.
 [
   # ---- message-layer senders -------------------------------------------
   # The human at the dashboard: a broker recipient (the T4LK box sends