fix(gateway): log the foreign-standalone-owner warning once per start

decide() runs twice per start (the CLI guard in hermes_cli.gateway and again
from start_gateway -> _host_attach_or_none), and the lock-losing path in
_claim_host_gateway_role re-derives the same fact via _owner_is_standalone(),
so every boot of a generated unit beside another profile's standalone gateway
logged the "starting beside it" WARNING three times. decide() is a verdict
function; reporting belongs at the action site. Demote host_attach's copy to
INFO and keep run.py's lock-claim WARNING, which fires exactly once on both the
--replace and plain paths and carries the `gateway migrate --multiplex` hint.

The lifecycle test still asserts the converge hint is logged by decide(); it
now captures at INFO.

gateway/host_attach.py

@@ -381,9 +381,10 @@ def decide(our_home: Path, *, replace: bool = False) -> HostAttachDecision:
     if attached is not None and attached.standalone:
         # One-process-per-profile fleet: the owner is another profile's standalone gateway. Refusing
         # here exits 78, which every supervisor treats as permanent — on a launchd fleet that parked
-        # every unit but the first to claim the host lock. Start beside it; the host-lock claim logs
-        # the topology and the `gateway migrate --multiplex` path stays the way to converge.
-        logger.warning(
+        # every unit but the first to claim the host lock. Start beside it. decide() runs twice per
+        # start (CLI guard + start_gateway), so this is INFO; the host-lock claim in run.py logs the
+        # one WARNING with the `gateway migrate --multiplex` converge hint.
+        logger.info(
             "Another profile's standalone gateway owns this host (%s); starting profile '%s' beside it. "
             "Fold every profile onto one gateway with: hermes gateway migrate --multiplex",
             attached.describe(), profile)

tests/gateway/test_host_attach_lifecycle.py

@@ -159,7 +159,7 @@ def test_a_standalone_owner_is_the_per_profile_topology_not_a_refusal(tmp_path,
     monkeypatch.setattr("gateway.control_socket.rescan_gateway_profiles",
                         lambda home, timeout=8.0: {"multiplex": False, "served_profiles": ["tank"]})
 
-    with caplog.at_level("WARNING", logger="gateway.host_attach"):
+    with caplog.at_level("INFO", logger="gateway.host_attach"):
         assert host_attach.decide(tmp_path / "root" / "profiles" / "nous").outcome == host_attach.START
     assert any("migrate --multiplex" in r.getMessage() for r in caplog.records), "the converge hint is logged"
     assert asyncio.run(gateway_run._host_attach_or_none(replace=False)) is None