LUCI - file (config) web editor page

Are you talking about editing the raw text files? (the whole point of the LuCI interface is to have a way to edit the configuration files, but obviously this is with a GUI rather than raw text edits).

Two ways of doing this already exist (via the linux CLI piped up through the LuCI interface):

And it has been discussed in the past... the general consensus is to use an app on your computer (winscp, other methods) to transfer and edit the files).