Fix SharePopover positioning by using correct Melt UI popover pattern

Commit notes

- Changed floatingConfig from function to object form to match other working popover implementations (Header, WorkspaceSwitcher, SequencerTrack) - Removed external 'open' state management in favor of popover's internal state - Moved state reset logic to () that reacts to popover.open changes - This fixes the issue where the popover appeared at top-left of screen instead of positioned relative to the trigger button

Co-authored-by: armin.naimi <[email redacted]>