Fix normal, hover and pressed states for links on new-tab/home page

As per the normal Fx convention, links should be:

• normal by default
• underlined + one shade lighter (#FFD567 or proton yellow-30) on hover
• normal + another shade lighter (#FFEA80 or proton yellow-20) when pressed

(typically light theme goes darker on hover/pressed, but the foreground content is light on dark here)