Store Branding: Apply brand color to backend as well

[dennisreimann]

For now we only apply the store branding on public pages — this adds it to the store's backend as well. Closes #5990.

[dstrukt]

Looks good AFAICT.

tACK!

Another pair of eyes wouldn't hurt though

Few thoughts:

• if the user chooses a yellow, it might look bad on Light mode, etc... but i guess the user will figure this out pretty quickly, which leads me to...
• Also realizing i didn't test, but does just removing a custom HEX value default back to the BTCPAY green? we should probably have a way to opt back into the default

[dennisreimann]

does just removing a custom HEX value default back to the BTCPAY green?

Yes it does.

if the user chooses a yellow, it might look bad on Light mode

Vice versa with dark brand color in dark mode. Not sure if we want to touch this — in 1b7718e I made an attempt at it and adjust the colors based on the brightness of the brand color. I think it covers it well enough to be safe, but I'm not sure if it's wanted. Yet it might be better than the status quo, in which there are brand color and theme combinations, which would not work.

[dstrukt]

Ahh great - will take another look!

[dstrukt]

i think your solution handles the variability pretty well, we can always patch if we think of something better

tACK