Added Goal Count Feature and Improved XP System

I added a new feature that allows users to set goal counts for each juggling trick.

This makes it easier to define personalized practice targets.

I also updated the XP calculation system so that experience scales based on the goal count,
allowing fair progression even for tricks with smaller targets.

Additionally, goal counts are now displayed for each trick, making progress easier to track.

Step by step, the site is becoming more game-like and enjoyable for practice.