Ws 2975 fix sign in banner dialog announcation

[SantaZena]

Resolves JIRA: https://bbc.atlassian.net/browse/WS-2975

Summary

The "Sign in" button inside the Save Article sign-in modal was not descriptive enough for screen reader users — it just said "Sign in" with no context. This change makes screen readers announce "Sign in to My News" (or the service-localised equivalent) instead, while the button still visually displays "Sign in" for sighted users.

Code changes

• Added optional signInAccessibleLabel to the account translations type in translations.
• Added signInAccessibleLabel: Sign in to My News" to the ws and hindi service configU
• Updated AccountActionButtons to accept an optional signInAccessibleLabel prop
• Updated AccountSignInModal to read signInAccessibleLabel from translations and pass it to AccountActionButtons
• Created new test file for AccountActionButtons covering the accessible label behavior
• Created new test file for AccountSignInModal covering the accessible label behaviour

Testing

1. Open an article page on the hindi or ws service while signed out and with the personalisation toggle enabled
2. Click the Save button to open the sign-in modal
3. Using a screen reader (e.g. VoiceOver on macOS), navigate to the "Sign in" link inside the modal — it should announce "Sign in to My News" (hindi: "माय न्यूज़ में साइन इन करें"), not just "Sign in"
4. Visually confirm the button still displays "Sign in" as before
5. Check the same button in the AccountPromotionalBanner and My News guest page — it should still announce just "Sign in" with no change

Useful Links

https://www.dropbox.com/scl/fi/gc4na1b1ztcpql9iyyiq1/A11Y-Swarm-WS-Sign-in-pop-up-banner-trigger-Save-for-later.paper?rlkey=0uyxoi0fad6pq4zbsbtnmucvf&dl=0

[elvinasv]

Works well from the a11y point of view 👍
As talked offline, span wrapper invalidated flex positioning, but it's an easy fix

[elvinasv]

Good work! 👍

[LukasFrm]

LGTM!