Depends on D19149. Ref T13088. Since the new log requires a bunch of log reprocessing, the cutover is going to require at least some time for installs to run migrations. Add a link in the UI to ease the transition, smooth over some behaviors a little, and fix a fetch issue where we'd request past the end of the log (since this is now enforced).

Viewed a traditional Harbormaster build, saw links to the new standalone log pages.