Refactor modal (#18377)

## Summary

- Move Modal UI components (`Modal`, `ModalContent`, `ModalHeader`,
`ModalFooter`, `ModalBackdrop`) from `twenty-front` to `twenty-ui` as
stateless, reusable components
- Create `ModalStatefulWrapper` in `twenty-front` that connects Jotai
state (`isModalOpenedComponentState`) to the stateless `Modal` via an
`isOpen` prop
- Rename `modalVariant` prop to `overlay` with clearer values: `'dark'`
(default), `'light'` (in-container), `'transparent'` (invisible panel).
Remove unused `'medium'` overlay
- Rename `modalId` to `modalInstanceId` across the entire modal zone
(~30 consumer files)
- Extract `ModalProps` to its own file in
`twenty-ui/types/ModalProps.ts`; extract `ModalStatefulWrapperProps` to
its own file using `Pick<ModalProps, ...>` for shared props
- Extract `ModalBackdrop` to its own file and export from `twenty-ui`;
use it in `UserOrMetadataLoader` instead of a local styled component
- Use `ModalFooter` in `StepNavigationButton` and `ModalHeader` in
`SpreadsheetImportStepperContainer` instead of duplicated `styled.div`
definitions
- Remove unused `onClose` prop from stateless `Modal`; fix `typeof
document` guard in `ModalStatefulWrapper`
- Split shared types into individual files: `ModalSize.ts`,
`ModalPadding.ts`, `ModalOverlay.ts`
- Extract wyw profiling instrumentation from `vite.config.ts` into
reusable `createWywProfilingPlugin` with parametrized threshold and
improved logging
- Delete old `Modal.tsx`, `Modal.styles.ts`, `ModalContent.tsx`,
`ModalHeader.tsx`, `ModalFooter.tsx` from `twenty-front`
- Add comprehensive Storybook stories in `twenty-ui` covering Default,
Confirmation, Small, ExtraLarge, Closed, and Interactive variants

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