Summary: Removed pricing tiers for courses

Why It Matters: This change simplifies the pricing information shown to potential students.

What Changed:

• Removed detailed descriptions of "Базовый," "С куратором," and "С репетитором" pricing tiers.
• Removed the specific price for the "Базовый" tier.
• Updated the starting prices for all listed courses by increasing them by 50 rubles.
• Changed the image file name from "Image 159" to "Image 51" for the "Все материалы для подготовки" image.