When were remote repositories, for any package manager, invented and implemented?
I have not followed closely the history, but there was no big bang, only evolution. There were large software repository on the net in the early nineties, and probably even in the eighties. The archive CTAN for TeX started in 1992. Hobbes for OS/2 started around the same time, I think. There were some for Linuxes, for BSD Unices, for Windows, for TCL/Tk ... In the mid nineties they became available on DVD as many people did not get enough bandwidth to download from FTP archives. (company names include Infomagic, Pacific High tech, Walnut Creek, Prime Time Freeware, ...). Linux existed in distributions, and still does. People could download very early, if they had the bandwidth. Well organized packaging came progressively ... and required developping standards. The early packaging systems could not manage dependencies, and removing a package was a risky business. Keeping track of what was installed came in. And things slowly improved. Not that slowly when you think of it.
I should add that much of the technology relies on version management techniques that started evolving in the early eighties (probably late seventies), but not over the network. Possibly the earliest tool in that line is
make, designed by Stuart Feldman in 1977 at Bell Labs, and allegedly produced in a single night.
AFAIK FreeBSD ports is/are the mother(s) of all later online repositories, it dates to the early 90's: