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/steps/components/MatchColumnsStep/components/SubMatchingSelectDropdownButton.tsx

@@ -9,8 +9,7 @@ import { type SpreadsheetMatchedOptions } from '@/spreadsheet-import/types/Sprea
 import { getFieldOptions } from '@/spreadsheet-import/utils/getFieldOptions';
 import { styled } from '@linaria/react';
 import { useContext } from 'react';
-import { ThemeContext } from 'twenty-ui/theme';
-import { themeCssVariables } from 'twenty-ui/theme-constants';
+import { ThemeContext, themeCssVariables } from 'twenty-ui/theme-constants';
 import { Tag, type TagColor } from 'twenty-ui/components';
 import { IconChevronDown } from 'twenty-ui/display';
 import { type SelectOption } from 'twenty-ui/input';
@@ -31,12 +30,10 @@ export const SubMatchingSelectDropdownButton = ({
   column,
   placeholder,
 }: SubMatchingSelectDropdownButtonProps) => {
+  const { theme } = useContext(ThemeContext);
   const { spreadsheetImportFields: fields } = useSpreadsheetImportInternal();
   const options = getFieldOptions(fields, column.value) as SelectOption[];
   const value = options.find((opt) => opt.value === option.value);
-
-  const { theme } = useContext(ThemeContext);
-
   return (
     <SubMatchingSelectControlContainer cursor="pointer" id="control">
       <Tag

packages/twenty-front/src/modules/spreadsheet-import/steps/components/MatchColumnsStep/components/UnmatchColumnBanner.tsx

@@ -1,9 +1,8 @@
 import { styled } from '@linaria/react';
-import { useContext } from 'react';
 import { isDefined } from 'twenty-shared/utils';
 import { Banner, IconChevronDown, IconInfoCircle } from 'twenty-ui/display';
-import { ThemeContext } from 'twenty-ui/theme';
-import { themeCssVariables } from 'twenty-ui/theme-constants';
+import { useContext } from 'react';
+import { ThemeContext, themeCssVariables } from 'twenty-ui/theme-constants';
 
 const StyledBanner = styled(Banner)<{ allMatched: boolean }>`
   background: ${({ allMatched }) =>

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

@@ -1,6 +1,4 @@
 import { useCallback, useContext, useState } from 'react';
-import { ThemeContext } from 'twenty-ui/theme';
-
 import { useSpreadsheetImportInternal } from '@/spreadsheet-import/hooks/useSpreadsheetImportInternal';
 import { useSnackBar } from '@/ui/feedback/snack-bar-manager/hooks/useSnackBar';
 import { ModalContent } from 'twenty-ui/layout';
@@ -14,6 +12,7 @@ import { SelectHeaderStep } from './SelectHeaderStep/SelectHeaderStep';
 import { SelectSheetStep } from './SelectSheetStep/SelectSheetStep';
 import { UploadStep } from './UploadStep/UploadStep';
 import { ValidationStep } from './ValidationStep/ValidationStep';
+import { ThemeContext } from 'twenty-ui/theme-constants';
 
 type SpreadsheetImportStepperProps = {
   nextStep: () => void;
@@ -25,7 +24,6 @@ export const SpreadsheetImportStepper = ({
   prevStep,
 }: SpreadsheetImportStepperProps) => {
   const { theme } = useContext(ThemeContext);
-
   const { initialStepState } = useSpreadsheetImportInternal();
 
   const [currentStepState, setCurrentStepState] =