chore(twenty-front): migrate auth, activities, AI, pages and small modules from Emotion to Linaria (PR 2-3/10) (#18328)

## Summary

- Migrate ~200 files from `@emotion/styled` / `@emotion/react` to
`@linaria/react` + `themeCssVariables`, continuing the zero-runtime
CSS-in-JS migration (PR 2-3 of the [migration
plan](docs/emotion-to-linaria-migration-plan.md))
- Modules covered: **auth** (19), **activities** (53), **ai** (30),
**pages** (70), **action-menu** (3), **object-metadata** (4),
**onboarding** (2), **workspace** (2), **file** (3), **error-handler**
(2), **front-components** (1), **geo-map** (1), **loading** (5),
**testing** (5), plus a `style` prop addition to `TableRow`
- Handles `styled(FunctionComponent)<Props>` incompatibility with
Linaria by using CSS custom properties via `style` + `var()` references

## Test plan

- [x] `npx nx lint:diff-with-main twenty-front` passes
- [x] `npx nx typecheck twenty-front` passes
- [ ] Visual spot-check of auth, onboarding, settings, activities, and
AI chat screens
- [ ] No remaining `@emotion/styled` or `@emotion/react` imports in
migrated files


Made with [Cursor](https://cursor.com)

packages/twenty-front/src/loading/components/UserOrMetadataLoader.tsx

@@ -1,14 +1,15 @@
-import styled from '@emotion/styled';
+import { styled } from '@linaria/react';
 
 import { useShowAuthModal } from '@/ui/layout/hooks/useShowAuthModal';
 import { Modal } from '@/ui/layout/modal/components/Modal';
 import { NAVIGATION_DRAWER_CONSTRAINTS } from '@/ui/layout/resizable-panel/constants/NavigationDrawerConstraints';
 import { MOBILE_VIEWPORT } from 'twenty-ui/theme';
+import { themeCssVariables } from 'twenty-ui/theme-constants';
 import { LeftPanelSkeletonLoader } from '~/loading/components/LeftPanelSkeletonLoader';
 import { RightPanelSkeletonLoader } from '~/loading/components/RightPanelSkeletonLoader';
 
 const StyledContainer = styled.div`
-  background: ${({ theme }) => theme.background.noisy};
+  background: ${themeCssVariables.background.noisy};
   box-sizing: border-box;
   display: flex;
   flex-direction: row;