feat: add employee management, backend health check, and UI improvements

server/src/app/db/base.py

@@ -1,6 +1,17 @@
 from app.db.base_class import Base
 from app.models.approval import ApprovalRecord
+from app.models.employee_change_log import EmployeeChangeLog
 from app.models.employee import Employee
+from app.models.organization import OrganizationUnit
 from app.models.reimbursement import ReimbursementRequest
+from app.models.role import Role
 
-__all__ = ["Base", "Employee", "ReimbursementRequest", "ApprovalRecord"]
+__all__ = [
+    "Base",
+    "ApprovalRecord",
+    "Employee",
+    "EmployeeChangeLog",
+    "OrganizationUnit",
+    "ReimbursementRequest",
+    "Role",
+]