Make the landing page scrollable by arrow keys upon initial load

[ethanjli]

Previously, due to the way https://github.com/sargassum-world/styles had set up the CSS with divs and flexboxes to enable a responsive navbar (at the top or at the side, depending on page width), the main content wasn't scrollable by arrow keys upon first load. However, the (current version of) device-portal doesn't need a navbar, so we can easily make the main content full-height and make the html body scrollable by default. This PR does that, and upgrades the @sargassum-world/styles npm package to v0.3.0 so that the body scrollbar is no longer deleted (this is necessary because it's impossible to simply override a body::-webkit-scrollbar selector's display: none attribute).

This PR also:

• Removes the goreleaser release builds for darwin and windows, since the device-portal is specifically meant to be deployed on Linux-based PlanktoScopes anyways. We can still restore those builds in the future, if necessary, and we still have (non-required) CI build checks for those platforms.
• Improves the instructions for finding other PlanktoScopes, and moves those instructions into the "Need Help?" section.