Implement foreign key violation handling in EmployeesRepository delete methods

- Enhanced the `delete` and `bulkDelete` methods in `EmployeesRepository` to handle foreign key violations by throwing a `ConflictException` with a descriptive message.
- Added unit tests to verify that foreign key violations are correctly mapped to `ConflictException` and that unknown errors are rethrown as expected.
- Refactored error handling in the `delete` methods to improve clarity and maintainability.

src/modules/configuration/employees/employees.repository.spec.ts

@@ -220,6 +220,26 @@ describe('EmployeesRepository', () => {
     );
   });
 
+  it('delete maps foreign-key violations to ConflictException', async () => {
+    returning.mockRejectedValueOnce({ code: '23503' });
+    await expect(repository.delete('emp-1')).rejects.toMatchObject({
+      constructor: ConflictException,
+      message: 'Employee is referenced by other records',
+    });
+
+    returning.mockRejectedValueOnce({
+      cause: { code: '23503' },
+    });
+    await expect(repository.delete('emp-1')).rejects.toBeInstanceOf(
+      ConflictException,
+    );
+  });
+
+  it('delete rethrows unknown errors', async () => {
+    returning.mockRejectedValueOnce(new Error('db down'));
+    await expect(repository.delete('emp-1')).rejects.toThrow('db down');
+  });
+
   it('bulkUpdateStatus and bulkDelete return 0 for empty ids', async () => {
     await expect(
       repository.bulkUpdateStatus([], Status.create('active'), 'user-1'),
@@ -240,6 +260,16 @@ describe('EmployeesRepository', () => {
     await expect(repository.bulkDelete(['emp-1'])).resolves.toBe(1);
   });
 
+  it('bulkDelete maps foreign-key violations to ConflictException', async () => {
+    returning.mockRejectedValueOnce({
+      cause: { code: '23503' },
+    });
+    await expect(repository.bulkDelete(['emp-1'])).rejects.toMatchObject({
+      constructor: ConflictException,
+      message: 'Employee is referenced by other records',
+    });
+  });
+
   it('extendListQuery is a passthrough hook', () => {
     const qb = { join: true };
     expect(repository.extendListQuery(qb, { limit: 10, offset: 0 })).toBe(qb);