ui: Sidebar resizing improvements (#31119)
* ui : let the expanded sidebar be resized by dragging its edge
Bring back the desktop sidebar resize handle that was dropped with the
shadcn sidebar primitive. The width is clamped between 18rem and 32rem,
persists across reloads, and resets on a double-click of the handle. The
tab bar follows the same width so a wider sidebar never covers it.
Assisted by: Claude (Opus 5.5 Medium)
* ui : rubber-band the sidebar edge past its bounds and drag it shut
Past the max width the edge resists harder the further it is pulled, and
the same happens below the min width until the pull passes 9rem, where it
snaps to the pointer and letting go hides the sidebar. A release outside
the bounds springs the width back to the nearest one.
Assisted by: Claude (Opus 5.5 Medium)
* ui : show the sidebar edge strip faintly on hover and solid while dragging
The strip is clipped to the sidebar's rounded corners through its own
overlay, so the sidebar itself is never clipped.
Assisted by: Claude (Opus 5.5 Medium)
* ui : remember whether the desktop sidebar is open across reloads
A phone opens the sidebar as an overlay, so it always starts closed there
and its toggling never overwrites the desktop preference.
Assisted by: Claude (Opus 5.5 Medium)
* ui : fade the sidebar labels and conversation list with its width
The fade follows the live width, so it tracks both the toggle's width
transition and a drag below the minimum width.
Assisted by: Claude (Opus 5.5 Medium)
* ui : persist the sidebar width on release and clamp a restored one
A drag now updates only the live width and writes it to localStorage once
when released. A width restored from localStorage is clamped to the
current bounds, so a value saved under older bounds does not stick.
Assisted-by: Claude (Opus 5.5 Medium)
