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/ai/components/internal/AIChatContextUsageButton.tsx

@@ -1,11 +1,10 @@
 import { styled } from '@linaria/react';
 import { t } from '@lingui/core/macro';
 import { useLingui } from '@lingui/react/macro';
-import { useContext, useState } from 'react';
+import { useState } from 'react';
 import { isDefined } from 'twenty-shared/utils';
 import { HorizontalSeparator } from 'twenty-ui/display';
 import { ProgressBar } from 'twenty-ui/feedback';
-import { ThemeContext } from 'twenty-ui/theme';
 import { themeCssVariables } from 'twenty-ui/theme-constants';
 
 import { ContextUsageProgressRing } from '@/ai/components/internal/ContextUsageProgressRing';
@@ -116,7 +115,6 @@ const getCachedLabel = (lastMessage: AgentChatLastMessageUsage): string => {
 
 export const AIChatContextUsageButton = () => {
   const { t } = useLingui();
-  const { theme } = useContext(ThemeContext);
   const [isHovered, setIsHovered] = useState(false);
   const agentChatUsage = useAtomStateValue(agentChatUsageState);
 
@@ -175,19 +173,22 @@ export const AIChatContextUsageButton = () => {
               value={percentage}
               barColor={
                 percentage > 80
-                  ? theme.color.red
+                  ? themeCssVariables.color.red
                   : percentage > 60
-                    ? theme.color.orange
-                    : theme.color.blue
+                    ? themeCssVariables.color.orange
+                    : themeCssVariables.color.blue
               }
-              backgroundColor={theme.background.tertiary}
+              backgroundColor={themeCssVariables.background.tertiary}
               withBorderRadius
             />
           </StyledSection>
 
           {isDefined(lastMessage) && (
             <>
-              <HorizontalSeparator noMargin color={theme.background.tertiary} />
+              <HorizontalSeparator
+                noMargin
+                color={themeCssVariables.background.tertiary}
+              />
               <StyledSection>
                 <StyledSectionTitle>{t`Last message`}</StyledSectionTitle>
                 <SettingsBillingLabelValueItem
@@ -206,7 +207,10 @@ export const AIChatContextUsageButton = () => {
             </>
           )}
 
-          <HorizontalSeparator noMargin color={theme.background.tertiary} />
+          <HorizontalSeparator
+            noMargin
+            color={themeCssVariables.background.tertiary}
+          />
           <StyledSection>
             <StyledSectionTitle>{t`Conversation`}</StyledSectionTitle>
             <SettingsBillingLabelValueItem