Publish every version for free; kits come later

The project originally split into a free V1 and a paid V2 (STL files withheld from the public repository). We dropped that split: all designs, firmware and docs are published for free. In the short term, a donation link on the repository page is the only funding; selling ready-to-assemble kits is a possible later step. Licences that preserve the right to sell kits are still to be chosen. Once published, files cannot be un-published, so this is hard to reverse.