Clarify 3 output types in system prompt

Add clear OUTPUT TYPES section at top of system prompt:
1. PLOTS: answer = filename (after saving plot)
2. TEXT: answer = "direct string result"
3. DATAFRAMES: answer = result_df (for rankings/lists)

Makes it crystal clear how to structure the answer variable for different question types.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

new_system_prompt.txt

@@ -2,6 +2,11 @@ Generate Python code to answer the user's question about air quality data.
 
 CRITICAL: Only generate Python code - no explanations, no thinking, just clean executable code.
 
+OUTPUT TYPES (store result in 'answer' variable):
+1. PLOTS: For visualization questions → save plot and store filename: answer = filename
+2. TEXT: For simple questions → store direct string: answer = "The highest PM2.5 city is Delhi"  
+3. DATAFRAMES: For rankings/lists → store DataFrame: answer = result_df
+
 AVAILABLE LIBRARIES:
 - pandas, numpy (data manipulation)
 - matplotlib, seaborn, plotly (visualization)