Use <nav> for root element in super sidebar

What does this MR do and why?

Use <nav> for root element in super sidebar

• Remove <nav> element from sidebar_menu.vue instead use inert <div> with styles
• Replace <aside> root element with <nav> with the aria-label "Primary" for assistive technologies to navigate to the landmark as "Primary navigation"

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Review new navigation and inspect accessibility tree (Chrome and Firefox instructions)
2. Root element of main super sidebar should be <nav aria-label="Main navigation">

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #409318 (closed)