feat(combobox): refactor to support multi-selection.

[engijlr]

Summary

• Combobox now supports a multiple attribute for selecting multiple options
• Selected items appear as inline tags that flow alongside the text input
• Options show checkbox indicators in multi-select mode
• Search resets after each selection, Backspace removes the last selected tag
• Keyboard navigation (Arrow keys, Enter, Space) works for toggling options

Note on uui-input change

To support inline tags flowing with the text input, a default slot was added to uui-input inside a flex-wrap container. All existing input stories and all tests pass, but since this touches a foundational component it's worth extra attention during review.

[github-actions]

Hi there @engijlr, thank you for this contribution! 👍

While we wait for the team to have a look at your work, we wanted to let you know about that we have a checklist for some of the things we will consider during review:

• It's clear what problem this is solving, there's a connected issue or a description of what the changes do and how to test them
• The automated tests all pass (see "Checks" tab on this PR)
• The level of security for this contribution is the same or improved
• The level of performance for this contribution is the same or improved
• Avoids creating breaking changes; note that behavioral changes might also be perceived as breaking
• If this is a new feature, Umbraco HQ provided guidance on the implementation beforehand
• 💡 The contribution looks original and the contributor is presumably allowed to share it

Don't worry if you got something wrong. We like to think of a pull request as the start of a conversation, we're happy to provide guidance on improving your contribution.

If you realize that you might want to make some changes then you can do that by adding new commits to the branch you created for this work and pushing new commits. They should then automatically show up as updates to this pull request.

Thanks, from your friendly Umbraco GitHub bot 🤖 🙂

[sonarqubecloud]

Quality Gate passed

Issues
3 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud