Remove z-index tokens from tailwind config. With root `isolation: isolate`,
portaled overlays naturally sit above app content via DOM order.
- Tooltip / Popover / Dropdown: no z-index needed
- Dialog: z-50 (modal must cover non-modal portals)
- Toast: z-[99] (always on top, defined in toast component)
- Install @base-ui/react 1.2.0
- Define semantic z-index layer tokens (dropdown/popover/modal/toast/tooltip)
- Add TooltipProvider to root layout with global timing config
- Mark portal-to-follow-elem as deprecated with migration guide
- Enforce no-restricted-imports as error with suppression baseline
- Add ESLint rule to block new portal-to-follow-elem usage in business code
- Scaffold Phase 1 semantic primitives: Tooltip, DropdownMenu, Popover, Dialog
Part of #32767