Generated apps now run real Base UI components

DropdownMenu, Dialog, Popover, Select, Sheet, Tabs, Tooltip, Collapsible, and RadioGroup in your generated apps are now powered by the real Base UI components instead of hand-written shims. This brings proper keyboard navigation, focus management, exit animations, portaled content, collision-aware positioning, and real Sheet side-panels (previously Sheet was just a centered Dialog and the `side` prop did nothing). A compatibility translator keeps Radix-style patterns like `asChild` and `onSelect` working.