Fix board navigation from settings

[afurm]

Summary

• Reset the active view to the board whenever the Board workspace toggle is selected.
• Keep the Board toggle unselected while Settings is visible so the control can return users to the board.
• Add sidebar regression coverage for Settings -> Board navigation.

Root cause

Settings lived inside the board workspace mode, so the Board toggle could appear selected while Settings was still the active view. Selecting Board could then leave the view stuck on Settings, especially after switching through Chat or selecting a conversation.

Validation

• npm test -- src/client/components/Sidebar.test.tsx
• npm run typecheck
• npm test
• npm run build
• Rendered check on localhost: Settings -> Board and Settings -> Chat -> Board both returned to Board.