refactor(pipelock): move Docker-specific naming helpers to docker/pipelock.py

The three slug-based naming helpers were nominally on pipelock.py but
each assumed a Docker container topology (the container name is
'claude-bottle-pipelock-<slug>', the proxy URL uses that container
name). Move them next to DockerPipelockProxy:

  pipelock_container_name  -> claude-bottle-pipelock-<slug>
  pipelock_proxy_url       -> http://<container>:<port>
  pipelock_proxy_host_port -> <container>:<port>

backend.py imports them directly from .pipelock; the orphan-cleanup
test imports container_name from the same place.

claude_bottle/backend/docker/pipelock.py

@@ -12,10 +12,21 @@ from ...pipelock import (
     PIPELOCK_PORT,
     PipelockProxy,
     PipelockProxyPlan,
-    pipelock_container_name,
 )
 
 
+def pipelock_container_name(slug: str) -> str:
+    return f"claude-bottle-pipelock-{slug}"
+
+
+def pipelock_proxy_url(slug: str) -> str:
+    return f"http://{pipelock_container_name(slug)}:{PIPELOCK_PORT}"
+
+
+def pipelock_proxy_host_port(slug: str) -> str:
+    return f"{pipelock_container_name(slug)}:{PIPELOCK_PORT}"
+
+
 class DockerPipelockProxy(PipelockProxy):
     """Brings the pipelock sidecar up and down via Docker."""