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

LoopFit.Web/appsettings.json

@@ -5,5 +5,14 @@
       "Microsoft.AspNetCore": "Warning"
     }
   },
-  "AllowedHosts": "*"
+  "AllowedHosts": "*",
+  "ConnectionStrings": {
+    "DefaultConnection": "Host=localhost;Database=loopfit;Username=postgres;Password=postgres"
+  },
+  "Jwt": {
+    "Key": "LoopFitSuperSecretKeyThatIsAtLeast32CharactersLong!",
+    "Issuer": "LoopFit",
+    "Audience": "LoopFitApp",
+    "ExpirationMinutes": 60
+  }
 }