Compact the Projects sidebar into single-line rows

Document rows show only the name at the rail's shared 30px row height.
The generated description moves into a hover/focus card beside the rail
and stays available to assistive technology through aria-description.
Primary actions, project rows, document rows, children, Archived chats
and the account row now share one height, inset, gap and label column,
and the per-project New document button appears on that row's hover or
focus only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>