add backend source code

backend/app/services/__init__.py

@@ -0,0 +1,15 @@
+from app.services.department_service import DepartmentService
+from app.services.staff_service import StaffService
+from app.services.indicator_service import IndicatorService
+from app.services.assessment_service import AssessmentService
+from app.services.salary_service import SalaryService
+from app.services.stats_service import StatsService
+
+__all__ = [
+    "DepartmentService",
+    "StaffService",
+    "IndicatorService",
+    "AssessmentService",
+    "SalaryService",
+    "StatsService",
+]