OP you might try posting this question in r/Archaeology

Star Carr is one of the oldest known houses in the world dating to about 11000 years ago. You could see if there are artifacts or other evidence of aesthetic decoration of dwellings at their website. http://www.starcarr.com/index.html

My hunch is that shelter appearance became important at the same time humans began using caves for shelter/homes which was thousands of years before Star Carr. I say this because Lascaux and other even older ancient caves have wall paintings. It is believed Lascaux was not a dwelling but its wall art nevertheless indicates interior aesthetics mattered.