[RFF] Homepage: improvement for the search card

[g123k]

Hi everyone!

Here are some improvements for the search card that I've worked on, and I need your advice before submitting it as a PR.
The idea is to better show the brand, always show the tagline (which will be replaced with news in the future), and provide information about what to do.

Basically, the bottom text suggests scanning a product or swiping between cards, which can be counterintuitive for newcomers.
The hint for the search is more clear (instead of a vague "Search").

In light mode:

In dark mode:

[teolemon]

superseded by #5319