appview: have "y" keybind canonicalize the URL #511

GitHub has a handy keyboard shortcut I use all the time: on any page with a ref in the URL, you can press "y" and it canonicalizes the URL.

E.g.:

https://tangled.org/mitchellh.com/test/blob/main/.tangled/workflows/test.yml

would replace "mitchellh.com" with the did and "main" with the SHA (and maybe "test" with the did in the future too).

Its very good for sharing permalinks with people.