I'm in the process of collecting and documenting some Mermaid examples in a gist before I propose we standardize on them for documentation in my various communities.
Currently, the Github version of Mermaid (inside their Github-Flavored Markdown renderer) doesn't seem to support any indication that a Mermaid label can have a hyperlink (and they don't seem to support your tooltips hints at all). I've tried adding some extended ASCII (see #2869) to the labels such as the dagger † symbol, and that causes Mermaid to error out. (See my test example at #flowchart-with-hyperlinks.)
It isn't this community's responsibility to fix GitHub's deployment of your functionality, but I am seeking advice on how to possibly work around their bugs. Maybe some way of using the Mermaid styling capability to mark hyperlinked labels as being clickable (underlines? color?). I'm sure that someone has run into this before and has advice.