fix(VListItem): prevent navigation when disabled link is clicked

[mixelburg]

Fixes #22172

When a v-list-item has href or to (renders as <a>) and is disabled, clicking content inside a slot (e.g. a badge in the append slot) still causes the browser to follow the link.

The root cause: the onClick handler returns early when !isClickable.value (which covers the disabled case), but native anchor click behaviour fires independently of our handler — preventDefault() was never called.

Fix: call e.preventDefault() at the start of onClick when props.disabled is true. This is the same pattern used by other Vuetify components (e.g. VBtn) to block navigation on disabled link elements.

Added a browser test verifying that clicking a disabled list item with href does not navigate (event.defaultPrevented === true).

[J-Sek]

I can still focus the list item and click Enter to navigate