fix: recalculate popover anchor position on open

[2u841r]

Summary

• Fixes sort/filter dropdowns opening at wrong position after scrolling on /shows
• anchor.ts now listens for the popover toggle event and recalculates position when newState === 'open'

Root Cause

getBoundingClientRect() was only called on resize — never when the popover opened. After scrolling, the cached button position was stale.

Closes #2198

[vercel]

@2u841r is attempting to deploy a commit to the Syntax Team on Vercel.

A member of the Team first needs to authorize it.