feat(orchestrator): Implement Synthesizer node for final worker results integration

backend/tests/test_orchestrator_synthesizer.py

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+from unittest.mock import MagicMock, patch
+from ea_chatbot.graph.nodes.synthesizer import synthesizer_node
+from ea_chatbot.graph.state import AgentState
+from langchain_core.messages import AIMessage
+
+def test_synthesizer_node_success():
+    """Verify that the synthesizer node produces a final response."""
+    state = AgentState(
+        messages=[AIMessage(content="Worker 1 found data."), AIMessage(content="Worker 2 searched web.")],
+        question="What are the results?",
+        checklist=[],
+        current_step=0,
+        iterations=0,
+        vfs={},
+        plots=[],
+        dfs={},
+        next_action="",
+        analysis={}
+    )
+    
+    # Mocking the LLM
+    with patch("ea_chatbot.graph.nodes.synthesizer.get_llm_model") as mock_get_llm:
+        mock_llm = MagicMock()
+        mock_llm.invoke.return_value = AIMessage(content="Final synthesized answer.")
+        mock_get_llm.return_value = mock_llm
+        
+        result = synthesizer_node(state)
+        
+        assert len(result["messages"]) == 1
+        assert result["messages"][0].content == "Final synthesized answer."
+        assert result["next_action"] == "end"