Complete linaria migration (#18361)

## Summary

Completes the migration of the frontend styling system from **Emotion**
(`@emotion/styled`, `@emotion/react`) to **Linaria** (`@linaria/react`,
`@linaria/core`), a zero-runtime CSS-in-JS library where styles are
extracted at build time.

This is the final step of the migration — all ~494 files across
`twenty-front`, `twenty-ui`, `twenty-website`, and `twenty-sdk` are now
fully converted.

## Changes

### Styling Migration (across ~480 component files)
- Replaced all `@emotion/styled` imports with `@linaria/react`
- Converted runtime theme access patterns (`({ theme }) => theme.x.y`)
to build-time `themeCssVariables` CSS custom properties
- Replaced `useTheme()` hook (from Emotion) with
`useContext(ThemeContext)` where runtime theme values are still needed
(e.g., passing colors to non-CSS props like icon components)
- Removed `@emotion/react` `css` helper usages in favor of Linaria
template literals

### Dependency & Configuration Changes
- **Removed**: `@emotion/react`, `@emotion/styled` from root
`package.json`
- **Added**: `@wyw-in-js/babel-preset`, `next-with-linaria` (for
twenty-website SSR support)
- Updated Nx generator defaults from `@emotion/styled` to
`@linaria/react` in `nx.json`
- Simplified `vite.config.ts` (removed Emotion-specific configuration)
- Updated `twenty-website/next.config.js` to use `next-with-linaria` for
SSR Linaria support

### Storybook & Testing
- Removed `ThemeProvider` from Emotion in Storybook previews
(`twenty-front`, `twenty-sdk`)
- Now relies solely on `ThemeContextProvider` for theme injection

### Documentation
- Removed the temporary `docs/emotion-to-linaria-migration-plan.md`
(migration complete)
- Updated `CLAUDE.md` and `README.md` to reflect Linaria as the styling
stack
- Updated frontend style guide docs across all locales

## How it works

Linaria extracts styles at build time via the `@wyw-in-js/vite` plugin.
All expressions in `styled` template literals must be **statically
evaluable** — no runtime theme objects or closures over component state.

- **Static styles** use `themeCssVariables` which map to CSS custom
properties (`var(--theme-color-x)`)
- **Runtime theme access** (for non-CSS use cases like icon `color`
props) uses `useContext(ThemeContext)` instead of Emotion's `useTheme()`

packages/twenty-front/src/modules/ui/feedback/snack-bar-manager/components/SnackBar.tsx

@@ -19,8 +19,8 @@ import {
 } from 'twenty-ui/display';
 import { ProgressBar, useProgressAnimation } from 'twenty-ui/feedback';
 import { LightButton, LightIconButton } from 'twenty-ui/input';
-import { MOBILE_VIEWPORT, ThemeContext } from 'twenty-ui/theme';
-import { themeCssVariables } from 'twenty-ui/theme-constants';
+import { ThemeContext } from 'twenty-ui/theme';
+import { MOBILE_VIEWPORT, themeCssVariables } from 'twenty-ui/theme-constants';
 
 export enum SnackBarVariant {
   Default = 'default',

packages/twenty-front/src/modules/ui/feedback/snack-bar-manager/components/SnackBarProvider.tsx

@@ -7,9 +7,8 @@ import { useIsMobile } from '@/ui/utilities/responsive/hooks/useIsMobile';
 import { snackBarInternalComponentState } from '@/ui/feedback/snack-bar-manager/states/snackBarInternalComponentState';
 import { RootStackingContextZIndices } from '@/ui/layout/constants/RootStackingContextZIndices';
 import { useAtomComponentStateValue } from '@/ui/utilities/state/jotai/hooks/useAtomComponentStateValue';
-import { MOBILE_VIEWPORT } from 'twenty-ui/theme';
+import { MOBILE_VIEWPORT, themeCssVariables } from 'twenty-ui/theme-constants';
 import { SnackBar } from './SnackBar';
-import { themeCssVariables } from 'twenty-ui/theme-constants';
 
 const StyledSnackBarContainer = styled.div`
   bottom: ${themeCssVariables.spacing[3]};