Adjust the blog category tags design

[danilo-leal]

Heya! 👋 Love the Mintlify product and thought about opening this quickie here when I realized the repo was public. Hope that's okay! First one, too, so let me know if anything's wrong. 😊

This PR adds a few stuff for the blog's category tags:

• Design adjustments: thicker font for better legibility, background change on hover for both light & dark, a slight green background on the selected state for more visibility, transition for smoother interaction, and making them fully rounded to match with other buttons on the page.
• Accessibility treatment: make the tags a <button> instead of a <div>, add aria-label, and focus treatment.
• Layout: add flex-wrap to the container to fix them in mobile.