Character upgrade system!

Another major update!
Technically, it went live on Saturday, but I was too tired to put together a proper devlog, so I had to postpone it a bit.

The character upgrade system is now in place, along with the first new upgrade option - Psi Ops.

Currently, 8 out of 9 characters are prepared for release. However, the launch of the first one already exposed a few balance issues. We'll be addressing these problems with each new character release, aiming to refine the overall balance as we go. We're planning to introduce a new character every few days.

We also made some adjustments to the UI, specifically around how traits are added and displayed. Our previous setup turned out to be a bit counterintuitive, so this should make the process smoother.