Improve link to validator on the homepage

[bugsbunnies]

As discovered by @ckniffen, currently the link to validator is barely visible on the Explorer homepage, dark text on a dark bg is terrible for accessibility.

Instead can we move the link into the tooltip once a user clicks a validator pill, they'll then be able to click on the link inside the tooltip to get to the validator. This will mean the tooltip has to persist once a user clicks on a pill and not disappear, once user clicks on pill again, the tooltip will no longer be persistent and go back to a 'appear on hover only' state.

Existing:

Propsed: