fix: JSON password field uses wrong variable (copy-paste bug)

[Shuu-37]

Summary

One-line fix for a copy-paste bug in --json mode that causes login to always fail.

The Bug

In main.cpp line 570, g_Password is set from maybeUsername instead of maybePassword:

auto maybeUsername = jsonGet<std::string>(jsonData, "username");
auto maybePassword = jsonGet<std::string>(jsonData, "password");

globals::g_Username = maybeUsername.value_or(globals::g_Username);
globals::g_Password = maybeUsername.value_or(globals::g_Password);  // BUG

This silently sets the password to the username when using --json mode, so authentication always fails.

The Fix

- globals::g_Password = maybeUsername.value_or(globals::g_Password);
+ globals::g_Password = maybePassword.value_or(globals::g_Password);

Impact

Anyone using --json mode for automated/launcher login is affected. CLI --user/--pass args are not affected (they use a separate code path).