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> [!IMPORTANT]
> Enhance `SelectedTeamSwitcher` to support nullable teams and add
'personal' team icon in `TeamIcon`, with updated translations.
>
> - **Behavior**:
> - `SelectedTeamSwitcher` in `selected-team-switcher.tsx` now supports
nullable teams with `allowNull` prop and `nullLabel` for display.
> - `onChange` callback added to `SelectedTeamSwitcher` to handle team
changes.
> - `TeamIcon` in `team-icon.tsx` now supports a 'personal' team type,
displaying a default icon.
> - **Translations**:
> - Added translation key for "Personal team" in
`quetzal-translations.ts`.
> - **Misc**:
> - Updated `SelectedTeamSwitcherProps` type to handle nullable teams
and added `onChange` callback.
> - Minor refactoring in `selected-team-switcher.tsx` for better
handling of team selection logic.
>
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---------
Co-authored-by: Konsti Wohlwend <n2d4xc@gmail.com>
Updates `examples/demo` to Next.js 15 and adds Next.js 15 support to `packages/stack`.
The other packages and apps are still running on Next.js 14 to ensure compatibility.
