feat(drawer): add nested drawer support with vaul-svelte NestedRoot

Commit notes

- Add 'nested' prop to Drawer component for proper drawer stacking - When nested=true, use Drawer.NestedRoot which allows parent drawer to scale down and the nested drawer to appear on top - Update ShareDialog to use nested=true since it's always opened from within another drawer (SampleEditDrawer or PackEditDrawer) - Move ShareDialog inside parent drawer content in SampleEditDrawer for proper vaul context inheritance - The dismissible prop is forwarded to handle clicking outside to close

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