- Extract the optimistic + debounced-flush feed-priority flow into a shared
useChannelPriority hook (mirrors useChannelTagActions); the manager and the
channel-detail page now share it instead of two drifting copies.
- NavSidebar: drop the always-true `slim` const and its dead expanded-rail
branches; refresh the now-stale pinned/collapsible comments.
- Remove the orphaned `navCollapsed` localStorage key (no readers/writers left
after the always-slim rail).
- Channel page: drop the wrapper native `title` that duplicated PriorityStepper's
own Tooltip.
The keyboard-focus nav-label finding needed no change: the popover platform
already wires useFocus (visibleOnly), so a real Tab press shows the flyout label
(verified in-browser).