feat(plugin-system): add workflow pipeline and cross-plugin service registry

src/plugin_system/base/workflow_errors.py

@@ -0,0 +1,14 @@
+from enum import Enum
+
+
+class WorkflowErrorCode(Enum):
+    """Workflow统一错误码"""
+
+    PLUGIN_NOT_READY = "PLUGIN_NOT_READY"
+    STEP_TIMEOUT = "STEP_TIMEOUT"
+    BAD_PAYLOAD = "BAD_PAYLOAD"
+    DOWNSTREAM_FAILED = "DOWNSTREAM_FAILED"
+    POLICY_BLOCKED = "POLICY_BLOCKED"
+
+    def __str__(self) -> str:
+        return self.value