Add habit category images to the HabitCard component

[tsimian]

• For each of the 5 categories (Recycle, Commute, Water, Energy, and Food) an image representing the category should be displayed on the card.
• The images themselves will be stored in the images folder in the public directory and named after the related category.
• In the HabitCard component, use MUI’s CardMedia and set the src to the appropriate category.