feat(fase4): add NodeExecutor architecture with basic nodes

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/flow-engine/app/nodes/base.py

@@ -0,0 +1,34 @@
+from abc import ABC, abstractmethod
+from typing import Optional, Any
+from app.context import FlowContext
+
+
+class NodeExecutor(ABC):
+    """Base class for all node executors"""
+
+    @abstractmethod
+    async def execute(
+        self,
+        config: dict,
+        context: FlowContext,
+        session: Any
+    ) -> Optional[str]:
+        """
+        Execute the node logic.
+        Returns: branch name for routing (e.g., "default", "true", "false")
+                 or "wait" to pause execution
+        """
+        pass
+
+
+class NodeRegistry:
+    """Registry of all available node executors"""
+    _executors: dict = {}
+
+    @classmethod
+    def register(cls, node_type: str, executor: NodeExecutor):
+        cls._executors[node_type] = executor
+
+    @classmethod
+    def get(cls, node_type: str) -> Optional[NodeExecutor]:
+        return cls._executors.get(node_type)