Identify a small spider from southern Poland / eastern Europe
It is a Barn Funnel Weaver (Tegenaria domestica), In Europe it is known as the domestic house spider.
Here's some photos of this species to prove the similarities:


What caught my eye in particular that made it more clear that it was this species was the color patterns on the abdomen and cephalothorax, the size you mentioned, the shape of the feelers as well as the location.
The slight difference in shade of color may be due to being a different variety of the species or simply because of the weather and habitat that the spider is in.