Add event check in to Welcome landing page

[bconti123]

Fixes #2106

What changes did you make and why did you make them ?

• Added the event check-in feature to the Welcome landing page.
• Updated the check-in styles to closely match the Figma design.
• Refactored the code to improve readability and maintainability.

Notes:

• The "Manually Edit Events Check In" list is not populating yet. For now, you can update MongoDB directly by setting checkInReady: true on the event document.
• Check the event query and ensure checkInReady is true.

Screenshots of Proposed Changes Of The Website (if any, please do not screen shot code changes)

Visuals before changes are applied

Visuals after changes are applied

[Copilot]

Pull request overview

Adds an event check-in section to the logged-in Welcome landing page, including fetching checkInReady events and posting check-ins, with styling aligned to the existing check-in UI.

Changes:

• Fetches checkInReady=true events on the Welcome page and displays a meeting selector.
• Adds a CHECK IN action that POSTs to /api/checkins and renders a success state.
• Introduces new local styling constants for the check-in section and empty-state messaging.

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[bconti123]

Thanks! I’ve started addressing the feedback.

[bconti123]

Updated based on your feedback. Let me know if I missed anything.