implement Clean Architecture and user authentication

- Add LoopFit.Domain with entities (ApplicationUser, Workout, CalorieEntry, VitalData), enums (WorkoutType), and interfaces (IJwtTokenGenerator, IUserRepository, IWorkoutRepository)
- Add LoopFit.Application with auth DTOs, service interfaces, and DI setup
- Add LoopFit.Infrastructure with EF Core DbContext (PostgreSQL), ASP.NET Core Identity, JWT token generation, and repository implementations
- Add AuthController with register/login/me endpoints and JWT Bearer auth
- Add MAUI auth services (AuthService, TokenStorageService) and Login/Register Blazor pages

src/LoopFit.Domain/Entities/CalorieEntry.cs

@@ -0,0 +1,11 @@
+namespace LoopFit.Domain.Entities;
+
+public class CalorieEntry
+{
+    public Guid Id { get; set; }
+    public Guid UserId { get; set; }
+    public string Name { get; set; } = string.Empty;
+    public int Calories { get; set; }
+    public DateTime Date { get; set; } = DateTime.UtcNow;
+    public string? Notes { get; set; }
+}