Replace Moment.js with date-fns across Deck codebase

[Aditi76117]

• Resolves: Switch from moment.js to date-fns #1964
• Target version: main

Summary

This PR replaces all usages of Moment.js with date-fns across the Deck frontend codebase.
The change aims to modernize date handling, reduce bundle size, and align with Nextcloud’s current JavaScript practices.

All affected files using moment imports were updated to equivalent date-fns functions, and basic tests confirm correct rendering of due dates and relative timestamps in the UI.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Verified basic UI functionality for date rendering (due dates, relative dates)
• Documentation update not required

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