Localhost
Also called 127.0.0.1, Loopback
A name that always means this same computer. A server on localhost:5173 answers you and nobody else, because for anyone else the same name means their own machine.
An agent saying "it's running on localhost" has only told you about its own machine. If it runs in a container (a sealed-off environment on your machine) or in the cloud (on someone else's computer), its localhost isn't yours and you won't see a thing. Working on localhost also says little about production, where there's real distance, real encryption and a different server.
“Start the dev server and give me the exact URL it printed, because Vite picks another port if 5173 is taken. Then curl that URL and show me the status code before you tell me it works. Don't bind to 0.0.0.0.”