Update auth portal metadata for SEO and branding

[JoseSzycho]

Issue: Update SEO metadata for auth.datum.net

Description

The current metadata for the authentication portal (https://auth.datum.net) needs to be updated to better reflect our branding and provide a clearer experience for users in search results and browser tabs.

Proposed Changes

Please update the HTML head metadata to the following:

• Meta Title: Sign in - Datum Cloud Platform
• Meta Description: Securely access your Datum Cloud platform

Actual metadata

[JoseSzycho]

This was requested here: https://datum-inc.slack.com/archives/C084W6XRVS7/p1768837186310069