feat: Prevent notification errors for unauthenticated users

[seer-by-sentry]

Fixes BLT-JAVASCRIPT-40-DH. The issue was that: Unauthenticated users cause JavaScript to call addEventListener on null because notification elements are conditionally rendered only for authenticated users.

• Added a check to ensure notification elements exist before attempting to fetch notifications.
• This prevents errors for unauthenticated users who do not have these elements on the page.

This fix was generated by Seer in Sentry, triggered by DB. 👁️ Run ID: 1755520

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