feat(orchestrator): Harden VFS and enhance artifact awareness across workers

backend/src/ea_chatbot/graph/prompts/synthesizer.py

@@ -9,6 +9,7 @@ Your goal is to synthesize their individual findings into a single, cohesive, an
 - Do NOT mention the internal 'workers' or 'checklist' names.
 - Combine the data insights (from Data Analysts) and factual research (from Researchers) into a natural narrative.
 - Ensure all numbers, dates, and names from the worker reports are included accurately.
+- **Artifacts & Plots:** If plots or charts were generated, refer to them naturally (e.g., "The chart below shows..."). 
 - If any part of the plan failed, explain the status honestly but professionally.
 - Present data in clear formats (tables, bullet points) where appropriate."""
 
@@ -18,6 +19,9 @@ SYNTHESIZER_USER = """USER QUESTION:
 EXECUTION SUMMARY (Results from specialized workers):
 {worker_results}
 
+AVAILABLE ARTIFACTS:
+{artifacts_summary}
+
 Provide the final integrated response:"""
 
 SYNTHESIZER_PROMPT = ChatPromptTemplate.from_messages([