MSD Notifications: Add a clarifying link to Sites notifications settings to the Achievements toggle

[Copons]

Related to #112442

Proposed Changes

• Add a link to /me/notifications/sites from the global Achievements notifications card.

Before	After

Why are these changes being made?

The global Achievements notifications toggle was originally introduced in /reader/users/me/achievements, where it included (and still does) a link to /me/notifications, to clarify where to find site-level Achievements settings.

When the toggle was moved to `/me/notifications, the link was correctly dropped.

However, the MSD version of Notifications splits Sites and Extras settings. The Achievements setting is now in Extras, separated from Sites, so it needs the link again.

Testing Instructions

• Open https://my.wordpress.com/me/notifications/extras.
• Ensure the Achievements card contain a link to /me/notifications/sites.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• For UI changes, have you tested the affected components in dark mode?
• Have you tested accessibility for your changes? Ensure the feature remains usable with various user agents (e.g., browsers), interfaces (e.g., keyboard navigation), and assistive technologies (e.g., screen readers) (PCYsg-S3g-p2).
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

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[matticbot]

This PR does not affect the size of JS and CSS bundles shipped to the user's browser.

Generated by performance advisor bot at iscalypsofastyet.com.

[a8ci18n]

This Pull Request is now available for translation here: https://translate.wordpress.com/deliverables/34254783

Some locales (Hebrew) have been temporarily machine-translated due to translator availability. All other translations are usually ready within a few days. Untranslated and machine-translated strings will be sent for translation next Monday and are expected to be completed by the following Friday.

Thank you @Copons for including a screenshot in the description! This is really helpful for our translators.