Sidebar: no settings flash on the way into a repository, and a better slide
The repository menu is built from the address being gone to, so it is right from the first frame instead of the settings menu standing in until the page loads; its counts fill in when they arrive. The menus are two layers now: the arriving one slides in over the full width while the leaving one drifts a quarter of the way and fades, and moving between two far-side menus crossfades in place.
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