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/Components/Layout/MainLayout.razor

@@ -0,0 +1,34 @@
+@inherits LayoutComponentBase
+
+<div class="page">
+    <div class="sidebar">
+        <NavMenu/>
+    </div>
+
+    <main>
+        <div class="top-row px-4">
+            <a href="" @onclick="Logout" @onclick:preventDefault>Abmelden</a>
+        </div>
+
+        <article class="content px-4">
+            @Body
+        </article>
+    </main>
+</div>
+
+<div id="blazor-error-ui" data-nosnippet>
+    An unhandled error has occurred.
+    <a href="." class="reload">Reload</a>
+    <span class="dismiss">🗙</span>
+</div>
+
+@code {
+    [Inject] private Services.AuthService AuthService { get; set; } = default!;
+    [Inject] private NavigationManager Navigation { get; set; } = default!;
+
+    private async Task Logout()
+    {
+        await AuthService.LogoutAsync();
+        Navigation.NavigateTo("/login", forceLoad: true);
+    }
+}