fix: use lazy initialization for Docker client to prevent hanging in test environment

dashboard/backend/routers/docker_router.py

@@ -4,11 +4,20 @@ from config import DOCKER_HOST
 from rbac import require_admin
 
 router = APIRouter()
-client = docker.DockerClient(base_url=DOCKER_HOST)
+
+_client = None
+
+def get_docker_client():
+    """Get or create Docker client (lazy initialization)."""
+    global _client
+    if _client is None:
+        _client = docker.DockerClient(base_url=DOCKER_HOST)
+    return _client
 
 
 @router.get("/containers")
 def list_containers():
+    client = get_docker_client()
     return [
         {
             "id": c.short_id,
@@ -26,6 +35,7 @@ def list_containers():
 def container_action(container_id: str, action: str):
     if action not in ("start", "stop", "restart"):
         return {"error": "invalid action"}
+    client = get_docker_client()
     c = client.containers.get(container_id)
     getattr(c, action)()
     return {"ok": True}
@@ -33,5 +43,6 @@ def container_action(container_id: str, action: str):
 
 @router.get("/containers/{container_id}/logs")
 def container_logs(container_id: str, tail: int = Query(200, le=10000)):
+    client = get_docker_client()
     c = client.containers.get(container_id)
     return {"logs": c.logs(tail=tail, timestamps=True).decode(errors="replace")}