Closes#566.
The admin sidebar showed the running frontend + backend versions as
plain text. Wraps each version (and the "update available" indicator)
in an anchor pointing at the corresponding GitHub release tag, opening
in a new tab so the admin session isn't disrupted.
A small githubReleaseUrl helper (extracted to its own module for
testability) does the version → URL mapping. Because release-please
tags every release as `vX.Y.Z[-beta.N]`, the version string already
carries the channel suffix and a pure template covers both stable and
beta without branching.
Three unit tests pin the URL template — stable, beta-with-suffix, and
a defensive check that the leading `v` isn't double-prefixed if a
caller accidentally passes a tag-shaped value.
Paul Nothaft
d231623c59