fix(dashboards): resolve nested interactive elements in list-leaf-item

[harsha573252]

Frontend Pull Request Description

Fixes NUI-6284 - Removes nested interactive elements in list-leaf-item component (WCAG 4.1.2 violation).

What changed:

Anchor tag was nested inside a button div - now they're independent siblings.
Navigate button is absolutely positioned to cover the row via z-index layering.
Template and styling only.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have updated change log
• I have been following Definition of done
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new lint warnings
• New and existing unit tests pass locally and on CI with my changes
• Any dependent changes have been merged and published in downstream modules

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Additional Context (if necessary)