Did Nāgārjuna describe features of the Fourier transform?
Nāgārjuna was not a mathematician; he was an eminent buddhist philosopher. That is certainly enough, don't you think?
There is an interesting parallel here, perhaps — maybe even a useful analogy, though one that would only be meaningful to people who understand Fourier transforms — but that's all. The claim inside the question asked is mere puffery (great word, puffery), but if we puff Nāgārjuna up with undeserved praise we deflate that which he actually deserves praise for.
A thousand people can all look at the same thing and describe it in a thousand different ways. Laozi described it centuries before Nāgārjuna, but we wouldn't give Laozi credit for Nāgārjuna's vision, and we shouldn't give Nāgārjuna credit for Fourier's vision.