* [x] Put back persistence of sidebar open state
* [x] when agent panel is docked right, put sidebar on the right side
* [x] remove stale entries from `SidebarsByWindow`

Release Notes:

- N/A

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Co-authored-by: Eric Holk <eric@zed.dev>
Co-authored-by: Mikayla Maki <mikayla.c.maki@gmail.com>
Co-authored-by: Anthony Eid <hello@anthonyeid.me>