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/spreadsheet-import/utils/__tests__/csvSecurity.test.ts

@@ -1,8 +1,8 @@
 import { CSV_DANGEROUS_CHARACTERS } from '@/spreadsheet-import/constants/CsvDangerousCharacters';
 import { CSV_INJECTION_PREVENTION_ZWJ } from '@/spreadsheet-import/constants/CsvInjectionPreventionZwj';
-import { cleanZWJFromImportedValue } from '../cleanZWJFromImportedValue';
-import { containsCSVProtectionZWJ } from '../containsCSVProtectionZWJ';
-import { sanitizeValueForCSVExport } from '../sanitizeValueForCSVExport';
+import { cleanZWJFromImportedValue } from '@/spreadsheet-import/utils/cleanZWJFromImportedValue';
+import { containsCSVProtectionZWJ } from '@/spreadsheet-import/utils/containsCSVProtectionZWJ';
+import { sanitizeValueForCSVExport } from '@/spreadsheet-import/utils/sanitizeValueForCSVExport';
 
 describe('csvSecurity', () => {
   describe('CSV_DANGEROUS_CHARACTERS regex', () => {