Redmine

I made this quick patch more as some kind of preparation for #31353 (you may also add to this ticket to #31353 as related).
I think search bar and project selector elements will make more sense in the top bar, if avatar with user options fly-out will be added to the top bar. That's because top bar will have to become larger, hence to utilize available space more efficiently search bar and project selector might need to be moved to the top bar.

How it will look after the patch is applied

To win back some vertical space, we could also reduce the height of header later on, and even more space could be won if, as Bernhard suggested, we could combine the application header title with project breadcrumbs later on.

P.S. I didn't mess with floating rules in this patch, so bars are still floating left for now. I think floating could then also be adjusted a bit later.