Deprecate runtime theme objects in favor of CSS variables (#18402)

## Summary

- **Eliminate `ICON_SIZES` / `ICON_STROKES` constants**: all icon
dimensions are now resolved at runtime via
`resolveThemeVariableAsNumber(themeCssVariables.icon.size.X)`, ensuring
values always come from computed CSS variables
- **No more consumer imports from `twenty-ui/theme`**: moved
`ColorSchemeContext`, `ColorSchemeProvider`, `ThemeColor`,
`MAIN_COLOR_NAMES`, `getNextThemeColor`, `AnimationDuration` to
`twenty-ui/theme-constants`
- **Remove `ThemeContext` / `ThemeContextProvider` / `ThemeProvider` /
`ThemeType`**: replaced across ~300 files with `themeCssVariables` (for
CSS contexts) or `resolveThemeVariable` / `resolveThemeVariableAsNumber`
(for JS runtime values)
- **Simplify provider chain**: only `ColorSchemeProvider` remains — it
toggles `light`/`dark` class on `document.documentElement` and provides
`colorScheme` via React context
- **Fix pre-existing test failures**: `useIcons.test.ts`
(non-configurable ES module spy) and
`turnRecordFilterGroupIntoGqlOperationFilter.test.ts`
(`Omit<RecordFilter, 'id'>` type mismatch)

### Theme access pattern (before → after)

| Context | Before | After |
|---------|--------|-------|
| CSS (Linaria) | `${({ theme }) => theme.font.color.primary}` |
`${themeCssVariables.font.color.primary}` |
| JS runtime (icon size, animation) | `theme.icon.size.md` /
`ICON_SIZES.md` |
`resolveThemeVariableAsNumber(themeCssVariables.icon.size.md)` |
| Color scheme check | `theme.name === 'dark'` |
`useContext(ColorSchemeContext).colorScheme === 'dark'` |

packages/twenty-front/src/modules/spreadsheet-import/components/SpreadsheetImportTable.tsx

@@ -2,10 +2,8 @@ import { styled } from '@linaria/react';
 import { useContext } from 'react';
 // @ts-expect-error  // Todo: remove usage of react-data-grid
 import DataGrid, { type DataGridProps } from 'react-data-grid';
-import { ThemeContext } from 'twenty-ui/theme';
-import { themeCssVariables } from 'twenty-ui/theme-constants';
-
 import { useSpreadsheetImportInternal } from '@/spreadsheet-import/hooks/useSpreadsheetImportInternal';
+import { ThemeContext, themeCssVariables } from 'twenty-ui/theme-constants';
 
 const StyledDataGrid = styled(DataGrid)`
   --rdg-background-color: ${themeCssVariables.background.primary};
@@ -132,9 +130,10 @@ export const SpreadsheetImportTable = <Data,>({
   onSelectedRowsChange,
   selectedRows,
 }: SpreadsheetImportTableProps<Data>) => {
+  const { colorScheme } = useContext(ThemeContext);
+
   const { rtl } = useSpreadsheetImportInternal();
-  const { theme } = useContext(ThemeContext);
-  const themeClassName = theme.name === 'dark' ? 'rdg-dark' : 'rdg-light';
+  const themeClassName = colorScheme === 'dark' ? 'rdg-dark' : 'rdg-light';
 
   if (!rows?.length || !columns?.length) return null;