Branch sorting in refs dropdown to show recently updated branches first

What does this MR do and why?

Branch sorting in refs dropdown to show recently updated branches first

Changes the default sort order for branches in the /refs endpoint from alphabetical to updated_desc, making recently active branches appear at the top of dropdowns in merge request forms and other branch selectors.

Tags continue to use alphabetical sorting as version numbers benefit from lexical ordering.

Branch dropdown in MR	Branches List

Resolves #561483 (closed)

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

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.