You are correct. This is the wrong forum for this question. You're looking for the "Hardware and Devices" forum.
What you're looking for is called a "captive portal". I don't know of any consumer routers on the shelf that support this out-of-the-box.
I do know that DD-WRT supports this. DD-WRT is freeware router firmware. You'd have to flash your router with this new software (if it's supported) and set it up yourself. You can find that
here[
^]. Google for "DD-WRT captive portal" for instructions on setting up the landing page.