feat: Welcome Modal for first login

[kmye]

As a user, I want to see a welcome modal on the portal so that I get introduced to what is available

Note: This modal is required only if we rollout EduPass + SI in November, this is to have feature parity of Student Insights before launching PG in Jan 2027

[tfx-currents]

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🌊 Managed by Currents · Task 02ad5965-420c-4273-b689-a5fa8434c69c

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[YimingIsCOLD]

Dismiss the modal when clicked on backdrop