How can I prepare myself for a career as a Quantitative Analyst (quant), given that I am at the beginning of my 2 year masters program in computer science and have no financial background whatsoever?

You probably shouldn't focus exclusively on a career in finance. The first thing that you need to do is to be an extremely good software developer.  There are other ways of being a quant, but since you are getting a masters in computer science, I think it would be better to focus on being a first-class computer programmer rather than being a first class statistician. The second thing is to get work experience as a first-class computer programmer, and read so mathematical finance books on the side. The bad news is that no one knows what the quant job market is going to look like in the future.  However, if it's good you'll get hired.  If it's terrible, then you will end up with a non-financial computer programming job.

Develop and execute some ideas on your own to find causal relationships in data sets that interest you. Discuss what you developed in interviews.

Create a list of companies that you would like to work for... then email every person on that list that is the manager of quant role.  Email them how you can add VALUE to their company.  You'll probably get rejected by some but accepted by others.

I am in a Software Developer myself with zero knowledge of Algorithmic Trading/Computational Finance. As a beginner, I found this course super useful: https://www.coursera.org/course/compinvesting1