Improve selected state and keyboard navigation in DSO selector

[hernanhlagos]

References

• Fixes Active state indicator and keyboard navigation selecting a collection in Admin Search → Move Item #5529

Description

This PR fixes the visual state of the selected collection in the selector, when moving an item from one collection to another, and also fixes keyboard navigation in Safari.

Instructions for Reviewers

List of changes in this PR:

• Fixed the selected collection state by resolving the actual DSO id from listEntry.indexableObject.id instead of using listEntry['id'].
• Replaced the previous conditional class logic with Bootstrap’s active state, so the selected collection is clearly marked.
• Added helper methods to keep the selected-state logic out of the template.
• Added tabindex="0" to the list entries to fix a Safari issue where focus skipped the collection list and moved directly from the search input to the final action buttons.
• Used the @for $index to support keyboard navigation with ArrowDown and ArrowUp between collection entries in Safari.
• Added unit tests for selected DSO detection and keyboard focus navigation.

How to test:

1. Go to Admin Search.
2. Select an item and choose Move Item.
3. In the collection selector, select a collection.
4. Verify that the selected collection is clearly marked.
5. Select another collection and verify that the active state updates.
6. In Safari, use Tab from the search input and verify that focus enters the collection list instead of skipping to the final action buttons.
7. Use ArrowDown and ArrowUp to move through the collection entries.
8. Use Enter or Space to select the focused collection.

Note: I was not able to reproduce the keyboard navigation issue in Chrome, but I was able to reproduce and validate the fix in Safari.

Checklist

• My PR is created against the main branch of code (unless it is a backport or is fixing an issue specific to an older branch).
• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR passes [ESLint](https://eslint.org/) validation using npm run lint
• My PR doesn't introduce circular dependencies (verified via npm run check-circ-deps)
• My PR includes [TypeDoc](https://typedoc.org/) comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• My PR passes all specs/tests and includes new/updated specs or tests based on the [Code Testing Guide](https://wiki.lyrasis.org/display/DSPACE/Code+Testing+Guide).
• My PR aligns with [Accessibility guidelines](https://wiki.lyrasis.org/display/DSDOC9x/Accessibility) if it makes changes to the user interface.
• My PR uses i18n (internationalization) keys instead of hardcoded English text, to allow for translations.
• My PR includes details on how to test it. I've provided clear instructions to reviewers on how to successfully test this fix or feature.
• If my PR includes new libraries/dependencies (in package.json), I've made sure their licenses align with the [DSpace BSD License](https://github.com/DSpace/DSpace/blob/main/LICENSE) based on the [Licensing of Contributions](https://wiki.lyrasis.org/display/DSPACE/Code+Contribution+Guidelines#CodeContributionGuidelines-LicensingofContributions) documentation.
• If my PR includes new features or configurations, I've provided basic technical documentation in the PR itself.
• If my PR fixes an issue ticket, I've [linked them together](https://docs.github.com/en/issues/tracking-your-work/issues/linking-a-pull-request-to-an-issue).

[lgeggleston]

Thank you for putting up this pull request @hernanhlagos! You may have already seen, but this is currently failing a few build tests that will need to be fixed - looks like just minor linting errors though.