Create and save correlation heatmap

📂 Task: Generate a correlation matrix heatmap for numerical features.
📌 File to modify: main.ipynb

✅ Expected Output:

Use df.corr() and Seaborn’s heatmap() to plot
Save the plot using plt.savefig('heatmap.png')
Ensure labels, title, and color bar are visible

💡 This helps visualize relationships between features.

The work is in main.ipynb. Use pandas df.corr() to compute the correlation matrix and seaborn.heatmap() to plot it. Add labels, a title, and a color bar. Save the figure with plt.savefig('heatmap.png'). Run the notebook cell to generate and save the plot.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.