fix(collector): daemonize background subprocesses with start_new_session

Collector and mutator watcher subprocesses were spawned without
start_new_session=True, leaving them in the parent's process group.
SIGHUP (sent when the controlling terminal closes) killed both
processes silently — stdout/stderr were DEVNULL so the crash was
invisible.

Also update test_services and test_composer to reflect the ssh plugin
no longer using Cowrie env vars (replaced with SSH_ROOT_PASSWORD /
SSH_HOSTNAME matching the real_ssh plugin).

tests/test_composer.py

@@ -121,8 +121,8 @@ def test_service_config_http_server_header():
     assert env.get("SERVER_HEADER") == "nginx/1.18.0"
 
 
-def test_service_config_ssh_kernel_version():
-    """service_config for ssh must inject COWRIE_HONEYPOT_KERNEL_VERSION."""
+def test_service_config_ssh_password():
+    """service_config for ssh must inject SSH_ROOT_PASSWORD."""
     from decnet.config import DeckyConfig, DecnetConfig
     from decnet.distros import DISTROS
     profile = DISTROS["debian"]
@@ -131,7 +131,7 @@ def test_service_config_ssh_kernel_version():
         services=["ssh"], distro="debian",
         base_image=profile.image, build_base=profile.build_base,
         hostname="test-host",
-        service_config={"ssh": {"kernel_version": "5.15.0-76-generic"}},
+        service_config={"ssh": {"password": "s3cr3t!"}},
     )
     config = DecnetConfig(
         mode="unihost", interface="eth0",
@@ -140,7 +140,8 @@ def test_service_config_ssh_kernel_version():
     )
     compose = generate_compose(config)
     env = compose["services"]["decky-01-ssh"]["environment"]
-    assert env.get("COWRIE_HONEYPOT_KERNEL_VERSION") == "5.15.0-76-generic"
+    assert env.get("SSH_ROOT_PASSWORD") == "s3cr3t!"
+    assert not any(k.startswith("COWRIE_") for k in env)
 
 
 def test_service_config_for_one_service_does_not_affect_another():