How much of a bruising can a MTB take?
Assuming a decent and well maintained mountain bike it can handle much more abuse than riding up and down curbs or jumping around a bit. Even the most lightweight mountain bikes will not have the slightest problem with that.

However, two things are important: Good maintenance and riding technique! Riding on underinflated tires or a badly serviced suspension fork can easily lead to a flat or a bent rim when hitting hard on an edge. And good riding technique does not only make your riding look smoother but also is softer on your bike since it to some extent avoids the hardest impacts on your bike.

So go on with your riding, don't worry too much about how much your bike can handle, keep your bike well serviced and try to learn some decent riding technique.