App: Set a better secondary color

[algernon]

Instead of setting a grey-ish color as the secondary, which makes it hard to distinguish components using it from disabled ones, use a non-grey color instead.

The colors were chosen using https://www.canva.com/colors/color-wheel/, using the primary color as the basis. I wanted to choose a secondary that does not clash with the various alert colors.

So for light mode, I chose a blue-ish/purple-ish, darker color, and for dark mode, a more cyan-ish. They both feel okay with the primary keyboardio-orange.

Fixes #1089.

Old

New

[algernon]

Another option would be to use the same colors as for the Overview table highlight. I considered that, but that feels too close to the keyboardio-orange.

[obra]

The blues feel kind of garish to me. I'm happy to try to find alternate colors.

[algernon]

I'd appreciate that, I'm bad at colors.

[tlyu]

I tried softening them up a bit:

        main: darkMode() ? "#ed91f3" : "#ab0edd",

which is a slightly darker purple in light mode and a kind of lilac in dark mode.

[algernon]

Updated to use @tlyu's colors (thanks!), and merging as per @obra's ACK on Discord.