Enable non portalled rendering for popovers

[krokosik]

Fixes #610

Cause: this is a portal/layering interaction bug between Radix Popover and Vaul Drawer on mobile.

• In DateSelector, calendar is rendered in PopoverContent
• PopoverContent always portals to document.body
• On mobile, AppDrawer uses Vaul DrawerContent, which treats pointer events outside drawer content as outside interaction/dismiss.
• So when one taps a day, the tap target is in a portaled node outside the drawer subtree, and Vaul dismisses before react-day-picker selection runs.
• Desktop uses Radix Dialog, whose dismissable layer integration behaves better with portaled popovers.

This adds an option to render popovers without portals.