feat: Add announcement banner for MFA Release (M2-10461)

[jodybrookover]

• Tests for the changes have been added

  • Related documentation has been added / updated
  • OSS packages added to Curious open source credit page
  • Delivered the fix or feature branches into develop or release branches via Squash and Merge (to keep clean history)

  📝 Description

🔗 Jira Ticket M2-10461

Re-enables the AnnouncementBanner component (previously used for the rebranding campaign and then commented out) as an MFA launch announcement. The banner is now gated behind a LaunchDarkly flag (enable-admin-announcement-banner) so it can be toggled on/off without a deployment. Banner text lives in the i18n files (announcementBanner key) and the link URL is a named constant at the top of the component — the only changes needed for a future announcement campaign.

Changes include:

• Added enableAdminAnnouncementBanner feature flag to FeatureFlags type and FeatureFlagDefaults (default: false)
• Re-enabled in BaseLayout and AuthLayout (previously commented out)
• Updated AnnouncementBanner to gate rendering on the enableAdminAnnouncementBanner flag
• Updated announcementBanner i18n key in app-en.json and app-fr.json with MFA announcement copy
• Added useFeatureFlags mock to AnnouncementBanner.test.tsx so existing tests continue to pass

🪤 Peer Testing

To test with the LaunchDarkly flag:

• Ensure the enable-admin-announcement-banner flag exists in your target LD environment

• Enable the flag in LaunchDarkly

• Navigate to /auth/login (or any other /auth/ page before login)

• Navigate to to post-login page(s) (/dashboard/applets, /dashboard/managers, or /dashboard/respondents, etc)

• Expected outcome: Announcement banner appears at the top of the page with MFA messaging and a "Click to learn more" link

• Navigate to

• Dismiss the banner using the close button

• Expected outcome: Banner animates closed and does not reappear on refresh (dismissal is stored in localStorage per user)

• Disable the flag in LaunchDarkly

• Expected outcome: Banner does not appear on any route (no deployment required)

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[divbzero]

LGTM. Related to #2084 and #2155.