Add statistical libraries and update system prompt

- Add statsmodels and scikit-learn to requirements.txt for trend analysis
- Update system prompt with available libraries list
- Guide LLM to use appropriate libraries for statistical analysis
- Suggest simpler alternatives (numpy.polyfit) when possible

This resolves 'No module named statsmodels' errors for trend analysis queries.

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

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

requirements.txt

@@ -10,4 +10,6 @@ langchain_google_genai
 seaborn
 matplotlib
 pandas
-numpy
+numpy
+statsmodels
+scikit-learn

src.py

@@ -289,6 +289,16 @@ df["Timestamp"] = pd.to_datetime(df["Timestamp"])
 
 IMPORTANT: Only generate Python code - no explanations, no thinking, just clean code.
 
+AVAILABLE LIBRARIES:
+You can use these pre-installed libraries:
+- pandas, numpy (data manipulation)
+- matplotlib, seaborn, plotly (visualization) 
+- statsmodels (statistical modeling, trend analysis)
+- scikit-learn (machine learning, regression)
+- geopandas (geospatial analysis)
+Use appropriate libraries for trend analysis, regression, statistical tests, etc.
+For simple trends, prefer numpy.polyfit() over complex statistical libraries when possible.
+
 WHEN TO USE DIFFERENT OUTPUT TYPES:
 - Simple questions asking "Which city", "What month" (1-2 values) → TEXT ANSWERS (store text in 'answer')
 - Questions asking "Plot", "Show chart", "Visualize" → PLOTS (store filename in 'answer')