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/utils/string/__tests__/applySimpleQuotesToString.test.ts

@@ -1,4 +1,4 @@
-import { applySimpleQuotesToString } from '../applySimpleQuotesToString';
+import { applySimpleQuotesToString } from '~/utils/string/applySimpleQuotesToString';
 
 describe('applySimpleQuotesToString', () => {
   it('wraps the input string with single quotes', () => {

packages/twenty-front/src/utils/string/__tests__/pascalCase.test.ts

@@ -1,4 +1,4 @@
-import { pascalCase } from '../pascalCase';
+import { pascalCase } from '~/utils/string/pascalCase';
 
 describe('pascalCase', () => {
   it('converts a string to pascal case', () => {

packages/twenty-front/src/utils/string/__tests__/stripSimpleQuotesFromString.test.ts

@@ -1,4 +1,4 @@
-import { stripSimpleQuotesFromString } from '../stripSimpleQuotesFromString';
+import { stripSimpleQuotesFromString } from '~/utils/string/stripSimpleQuotesFromString';
 
 describe('stripSimpleQuotesFromString', () => {
   it('removes surrounding single quotes from a string', () => {

packages/twenty-front/src/utils/string/__tests__/turnIntoEmptyStringIfWhitespacesOnly.test.ts

@@ -1,4 +1,4 @@
-import { turnIntoEmptyStringIfWhitespacesOnly } from '../turnIntoEmptyStringIfWhitespacesOnly';
+import { turnIntoEmptyStringIfWhitespacesOnly } from '~/utils/string/turnIntoEmptyStringIfWhitespacesOnly';
 
 describe('turnIntoEmptyStringIfWhitespacesOnly', () => {
   it('should return an empty string for whitespace-only input', () => {

packages/twenty-front/src/utils/string/__tests__/turnIntoUndefinedIfWhitespacesOnly.test.ts

@@ -1,4 +1,4 @@
-import { turnIntoUndefinedIfWhitespacesOnly } from '../turnIntoUndefinedIfWhitespacesOnly';
+import { turnIntoUndefinedIfWhitespacesOnly } from '~/utils/string/turnIntoUndefinedIfWhitespacesOnly';
 
 describe('turnIntoUndefinedIfWhitespacesOnly', () => {
   it('should return undefined for whitespace-only input', () => {