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
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