feat: enforce @/ alias for imports and fix all relative parent imports (#16787)

## Summary
This PR enforces the use of `@/` alias for imports instead of relative
parent imports (`../`).

## Changes

### ESLint Configuration
- Added `no-restricted-imports` pattern in `eslint.config.react.mjs` to
block `../*` imports with the message "Relative parent imports are not
allowed. Use @/ alias instead."
- Removed the non-working `import/no-relative-parent-imports` rule
(doesn't work properly in ESLint flat config)

### VS Code Settings
- Added `javascript.preferences.importModuleSpecifier: non-relative` to
`.vscode/settings.json` (TypeScript setting was already there)

### Code Fixes
- Fixed **941 relative parent imports** across **706 files** in
`packages/twenty-front`
- All `../` imports converted to use `@/` alias

## Why
- Consistent import style across the codebase
- Easier to move files without breaking imports
- Better IDE support for auto-imports
- Clearer understanding of where imports come from

packages/twenty-front/src/modules/activities/utils/__tests__/filterAttachmentsToRestore.test.ts

@@ -1,5 +1,5 @@
 import { type Attachment } from '@/activities/files/types/Attachment';
-import { filterAttachmentsToRestore } from '../filterAttachmentsToRestore';
+import { filterAttachmentsToRestore } from '@/activities/utils/filterAttachmentsToRestore';
 
 describe('filterAttachmentsToRestore', () => {
   it('should not return any ids if there are no attachment paths to restore', () => {

packages/twenty-front/src/modules/activities/utils/__tests__/getActivityPreview.test.ts

@@ -1,4 +1,4 @@
-import { getActivityPreview } from '../getActivityPreview';
+import { getActivityPreview } from '@/activities/utils/getActivityPreview';
 
 describe('getActivityPreview', () => {
   it('should work for empty body', () => {

packages/twenty-front/src/modules/activities/utils/__tests__/getActivitySummary.test.ts

@@ -1,4 +1,4 @@
-import { getActivitySummary } from '../getActivitySummary';
+import { getActivitySummary } from '@/activities/utils/getActivitySummary';
 
 describe('getActivitySummary', () => {
   it('should work for empty body ""', () => {