Fix default selection for work items project selector

What does this MR do and why?

Fix default selection for work items project selector (#556029 (closed))

If frequent projects exists, default-select the first one

Changelog: fixed

References

• #556029 (closed)

Screenshots or screen recordings

Screen_Recording_2025-07-17_at_1.01.15_pm

How to set up and validate locally

1. Go to an epic, add a new issue child item and check the first frequent project is auto selected
2. Check http://127.0.0.1:3000/groups/flightjs/-/work_items/new as well

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #556029 (closed)