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()`

package.json

@@ -2,14 +2,13 @@
   "private": true,
   "dependencies": {
     "@apollo/client": "^3.7.17",
-    "@emotion/react": "^11.11.1",
-    "@emotion/styled": "^11.11.0",
     "@floating-ui/react": "^0.24.3",
     "@linaria/core": "^6.2.0",
     "@linaria/react": "^6.2.1",
     "@radix-ui/colors": "^3.0.0",
     "@sniptt/guards": "^0.2.0",
     "@tabler/icons-react": "^3.31.0",
+    "@wyw-in-js/babel-preset": "^1.0.6",
     "@wyw-in-js/vite": "^0.7.0",
     "archiver": "^7.0.1",
     "danger-plugin-todos": "^1.3.1",
@@ -41,6 +40,7 @@
     "lodash.snakecase": "^4.1.1",
     "lodash.upperfirst": "^4.3.1",
     "microdiff": "^1.3.2",
+    "next-with-linaria": "^1.3.0",
     "planer": "^1.2.0",
     "pluralize": "^8.0.0",
     "react": "^18.2.0",