The persisted mode (lh:tree-panel-mode) was read inside TreePanel — a
per-page component that remounts on every session navigation. First
paint rendered the SSR-safe "list" default, then the mount effect
applied the stored mode: with the animated frame, opening a session
visibly opened the panel and then closed it. The mode now lives in a
root-layout provider (the SidebarProvider pattern) and survives
navigations untouched — the panel mounts already in the right mode.
The default stays "list" so SSR and first client render agree; the
stored preference applies once, on provider mount.