refactor: 所有子图使用公共工具，避免重复造轮子

backend/app/agent_subgraphs/common/__init__.py

@@ -6,6 +6,7 @@
 - formatter: 格式化输出工具
 - intent: 意图理解工具
 - human_review: 人工审核工具
+- state_base: 状态基类工具
 """
 
 from .formatter import (
@@ -35,6 +36,13 @@ from .human_review import (
     ReviewManager
 )
 
+from .state_base import (
+    BaseState,
+    Phase,
+    TokenUsage,
+    StateUtils
+)
+
 __all__ = [
     # formatter
     "MarkdownFormatter",
@@ -56,5 +64,10 @@ __all__ = [
     "HumanReviewStore",
     "InMemoryReviewStore",
     "HumanReviewNode",
-    "ReviewManager"
+    "ReviewManager",
+    # state_base
+    "BaseState",
+    "Phase",
+    "TokenUsage",
+    "StateUtils"
 ]