Admin sidebar slides the whole page to the right on initial load

[ybnd]

Describe the bug

When you open/reload DSpace as an administrator, the admin sidebar animation plays, pushing the whole page to the right.

This is intentional to indicate when you log in, but on initial load it can look jarring if the animation plays immediately.

Making sidebar pinned state persistent amplifies this problem (see #3193)

Expected behavior

We should not trigger major animations on initial load when possible, especially for people that enable reduced motion.