Indeterminate checkbox in advanced table example

[bjarnef]

Description

A minor adjustment to set indeterminate property of "select all" checkbox, when any selection and not all items selected.

Inspiration:
https://ui.nuxt.com/docs/components/table
https://www.shadcn.io/patterns/data-table-standard-1
https://mui.com/material-ui/react-table/#data-table
https://storybooks.fluentui.dev/react/?path=/docs/components-table--docs#multiple-select

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (minor updates related to the tooling or maintenance of the repository, does not impact compiled assets)

Motivation and context

How to test?

Screenshots (if appropriate)

Checklist

• If my change requires a change to the documentation, I have updated the documentation in this pull request.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[github-actions]

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[sonarqubecloud]

Quality Gate passed

Issues
0 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

[Copilot]

Pull request overview

This PR enhances the advanced table example by adding indeterminate state support to the "select all" checkbox. The indeterminate state provides visual feedback when some (but not all) table rows are selected, following established UX patterns from libraries like shadcn and Nuxt UI.

Key Changes:

• Added indeterminate property binding to the select-all checkbox in the table header
• The indeterminate state activates when selection.length > 0 && selection.length < items.length

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