Spaces, off until turned on in Settings › Tabs

Separate sets of tabs in the one window, each with its own cookies and
sign-ins (a WebKit store of its own, made by identifier) and, if you
like, its own downloads folder. History, bookmarks, keychain passwords,
settings and extensions are shared. ⌃1–⌃9 switch, as in Arc, and a dot
of the space's colour before the tabs (beside the bookmarks in the
column) opens a menu: the spaces, new, rename, colour, downloads folder,
delete.

The first space is the session and store there always were, so turning
spaces on signs nobody out, and turning them off goes back to it. A
space left behind is parked: its sound paused, its tabs sleeping after
half an hour like any other. Deleting one closes its tabs and empties
its store at once; WebKit removes the store itself once this run lets go
of it, at the next launch at the latest.

bench: space [new NAME | go N | delete], ui spaces on|off, and strip
PATH [WIDTH] to draw the row of tabs off screen.

Closes #4

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