Add Skill navigation to Phase/ProjectSection, refactor logic

- Add Skill navigation properties to PhaseSection and ProjectSection, with EF Core mappings and migration for foreign keys and indexes.
- Refactor SetSkillFlags in GetProjectsListQueryHandler for clarity and efficiency; use eager loading for Skill.
- Add HasRemainingTime() to TaskSection and enforce time check in ChangeStatusSectionCommandHandler.
- Optimize EmployeeDocumentsRepository queries; add EmployeeId to WorkshopWithEmployeeDocumentsViewModel.
- Improve CustomExceptionHandler to handle FluentValidation exceptions and return proper status codes.
- Add FluentValidation package reference and perform minor code cleanups.

CompanyManagment.App.Contracts/EmployeeDocuments/WorkshopWithEmployeeDocumentsViewModel.cs

@@ -13,5 +13,6 @@ namespace CompanyManagment.App.Contracts.EmployeeDocuments
 		public string EmployerName { get; set; }
         public List<EmployeeDocumentItemViewModel> SubmittedItems { get; set; }
         public int EmployeesWithoutDocumentCount { get; set; }
+        public long EmployeeId { get; set; }
     }
 }