refactor(layout): account dropdown + propagate level context
Replace the standalone settings icon with an account dropdown on the
user icon (Settings + Log out). Soften the popover surface to a level-2
border + lighter shadow so it reads as a card-on-card surface. Have
Window and DropdownMenuContent publish their level into LevelContext so
nested controls pick the right contrast tones by intent rather than by
the default value.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>