refactor(standalone): 收敛 _STANDALONE 判断到 standalone_proxy 单一来源

各模块不再各自读 os.environ，统一从 standalone_proxy._STANDALONE 导入，
环境变量只在一处决定模式，减少散落的重复逻辑。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

kilostar/core/global_state_machine/global_state_machine.py

@@ -12,11 +12,9 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 
-import os
 from typing import Any, Dict, List, Optional, Tuple
-from kilostar.utils.standalone_proxy import actor_class
+from kilostar.utils.standalone_proxy import actor_class, _STANDALONE
 
-_STANDALONE = os.environ.get("KILOSTAR_MODE", "distributed") == "standalone"
 if not _STANDALONE:
     import ray
 

kilostar/core/global_state_machine/gsm_snapshot.py

@@ -30,11 +30,11 @@ GSM 仍然是 source of truth + 写入串行化器，但读路径解耦：
 from __future__ import annotations
 
 import asyncio
-import os
 from dataclasses import dataclass, field
 from typing import Any, Callable, Dict, List, Optional, Tuple
 
-_STANDALONE = os.environ.get("KILOSTAR_MODE", "distributed") == "standalone"
+from kilostar.utils.standalone_proxy import _STANDALONE
+
 if not _STANDALONE:
     import ray