Summary: Cursor adds mobile agent download option

Why It Matters: This change shows Cursor is expanding to mobile.

What Changed:

• The "Download for macOS" button was replaced with "Try mobile agent" in one spot.
• The code example for PyTorch MNIST Experiments was greatly expanded.
• The description for "Complete codebase understanding" was updated with new text.
• The "Try Cursor now" section now has "Try mobile agent" instead of a second "Download for macOS" button.