feat(ui): add desktop footer, legal custom link and about dialog

internal/api/handlers_auth.go

@@ -52,6 +52,8 @@ func (s *Server) handleAuthStatus(w http.ResponseWriter, r *http.Request) {
 			"hasImprintContent": s.cfg.Legal.ImprintContent != "",
 			"privacyUrl":        s.cfg.Legal.PrivacyURL,
 			"hasPrivacyContent": s.cfg.Legal.PrivacyContent != "",
+			"customLinkLabel":   s.cfg.Legal.CustomLinkLabel,
+			"customLinkUrl":     s.cfg.Legal.CustomLinkURL,
 		},
 	}
 	// Countdown to the next demo reset; seconds as well, so client clocks do not matter