Add open link in new tab

UX improvement suggestion: there's currently no easy way of opening a sidebar link in another tab by pressing Cmd+click or by right-clicking on the link and clicking Open In New Tab the way it normally works for all links. Currently the user is forced to copy the link, open a new tab, paste the link, and hit Enter – quite cumbersome. Fix this. Projects in the sidebar must become browsable links.   

Sidebar rail rows are now real links (stretched <a href>): Cmd/Ctrl/middle-click and right-click "Open link in new tab" work; plain click unchanged. Quick gate + rail tests green, visual check done (row unchanged). PR #6523 queued to the merge lane. Memory: none applied.