fix(profiles): correct misleading per-profile gateway port docstrings

The s6 profile-gateway docstrings claimed the bind port comes from a
`[gateway] port` key in config.yaml ("the single source of truth"). No such
key exists or is read anywhere — the API server port is resolved by
gateway/config.py from `API_SERVER_PORT` (or `platforms.api_server.extra.port`)
and defaults to 8642. The wrong reference actively misled a Docker user into
setting a non-functional `gateway.port`.

Point both docstrings (`S6ServiceManager._render_run_script`,
`_maybe_register_gateway_service`) at the real knob, and note the practical
consequence: since each supervised profile gateway loads its own HERMES_HOME,
two profiles left at the default both try to bind 8642 — each needs a distinct
`API_SERVER_PORT` in its own `.env`.

hermes_cli/profiles.py

@@ -1190,10 +1190,16 @@ def _maybe_register_gateway_service(profile_name: str) -> None:
     can re-register manually later via the gateway start command,
     which goes through the same dispatch path.
 
-    Port selection is governed by the profile's ``config.yaml``
-    (``[gateway] port = …``) — there is no Python-side allocator
-    (PR #30136 review item I5 retired the SHA-256-derived range
-    [9200, 9800) because it was dead code through the entire stack).
+    Port selection: each supervised profile gateway loads its own
+    ``HERMES_HOME`` and binds the port resolved by ``gateway/config.py``
+    from that profile's environment — ``API_SERVER_PORT`` (or
+    ``platforms.api_server.extra.port`` in the profile's
+    ``config.yaml``), defaulting to 8642. There is no ``[gateway] port``
+    key and no Python-side allocator (PR #30136 review item I5 retired
+    the SHA-256-derived range [9200, 9800) as dead code), so two
+    profiles that both leave the port at its default will both try to
+    bind 8642 — give each profile a distinct ``API_SERVER_PORT`` in its
+    ``.env``.
 
     Host short-circuit: check ``detect_service_manager()`` first and
     return immediately if it isn't ``"s6"``. This keeps host