chore(twenty-front): migrate small modules from Emotion to Linaria (PR 1/10) (#18314)

## Emotion → Linaria migration — PR 1 of 10

First batch of the `twenty-front` migration from Emotion (runtime
CSS-in-JS) to Linaria (zero-runtime, build-time extraction via
wyw-in-js). Covers **100 files** across 10 small standalone modules —
chosen as the lowest-risk starting point.

### Modules migrated

spreadsheet-import (28) · navigation-menu-item (17) · views (14) ·
billing (10) · blocknote-editor (7) · advanced-text-editor (7) ·
favorites (7) · navigation (4) · information-banner (3) ·
sign-in-background-mock (3)

### Migration pattern

Every file follows the same mechanical transformation:

| Emotion | Linaria |
|---|---|
| `import styled from '@emotion/styled'` | `import { styled } from
'@linaria/react'` |
| `${({ theme }) => theme.font.color.primary}` |
`${themeCssVariables.font.color.primary}` |
| `${({ theme }) => theme.spacing(4)}` |
`${themeCssVariables.spacing[4]}` |
| `const theme = useTheme()` | `const { theme } =
useContext(ThemeContext)` |
| `import { type Theme } from '@emotion/react'` | `import { type
ThemeType } from 'twenty-ui/theme'` |

`themeCssVariables` is a build-time object where every leaf is a
`var(--t-xxx)` CSS custom property reference, evaluated statically by
wyw-in-js. Runtime theme access (icon sizes, colors passed as props)
uses `useContext(ThemeContext)`.

### Gotchas encountered & fixed

- **Interpolation return types** — wyw-in-js requires `string | number`,
never `false`/`undefined`. Replaced `condition && 'css'` with `condition
? 'css' : ''`.
- **`css` tag inside `styled` templates** — Linaria `css` returns a
class name, not CSS text. Replaced with plain template strings.
- **`styled(Component)` needs `className`** — added `className` prop to
`NavigationDrawerSection`, `DropdownMenuItemsContainer`, and `Heading`.
- **`shouldForwardProp` not supported** — Linaria filters invalid DOM
props automatically for HTML elements. For custom components, used
wrapper divs where needed.
- **`FormFieldPlaceholderStyles`** — converted from Emotion `css`
function to a static string using `themeCssVariables`.

packages/twenty-front/src/modules/blocknote-editor/components/CustomSideMenuOptions.tsx

@@ -1,14 +1,16 @@
-import { useTheme } from '@emotion/react';
-import styled from '@emotion/styled';
+import { styled } from '@linaria/react';
+import { useContext } from 'react';
 import { type IconComponent } from 'twenty-ui/display';
+import { ThemeContext } from 'twenty-ui/theme';
+import { themeCssVariables } from 'twenty-ui/theme-constants';
 
 const StyledContainer = styled.div<{ Variant: Variants }>`
-  color: ${({ theme, Variant }) =>
-    Variant === 'danger' ? theme.color.red : 'inherit'};
+  color: ${({ Variant }) =>
+    Variant === 'danger' ? themeCssVariables.color.red : 'inherit'};
   align-items: center;
   display: flex;
   flex-direction: row;
-  gap: ${({ theme }) => theme.spacing(2)};
+  gap: ${themeCssVariables.spacing[2]};
 `;
 
 const StyledTextContainer = styled.div``;
@@ -26,7 +28,7 @@ export const CustomSideMenuOptions = ({
   Variant,
   text,
 }: CustomSideMenuOptionsProps) => {
-  const theme = useTheme();
+  const { theme } = useContext(ThemeContext);
   return (
     <StyledContainer Variant={Variant}>
       <LeftIcon