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.Application/Interfaces/IAuthService.cs

@@ -0,0 +1,10 @@
+using LoopFit.Application.DTOs.Auth;
+
+namespace LoopFit.Application.Interfaces;
+
+public interface IAuthService
+{
+    Task<AuthResponse?> RegisterAsync(RegisterRequest request);
+    Task<AuthResponse?> LoginAsync(LoginRequest request);
+    Task<AuthResponse?> GetCurrentUserAsync(Guid userId);
+}

src/LoopFit.Application/Interfaces/IFormFactor.cs

@@ -0,0 +1,7 @@
+namespace LoopFit.Application.Interfaces;
+
+public interface IFormFactor
+{
+    string GetFormFactor();
+    string GetPlatform();
+}