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/Controllers/AuthController.cs

@@ -0,0 +1,58 @@
+using System.Security.Claims;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using LoopFit.Application.DTOs.Auth;
+using LoopFit.Application.Interfaces;
+
+namespace LoopFit.Web.Controllers;
+
+[ApiController]
+[Route("api/[controller]")]
+public class AuthController : ControllerBase
+{
+    private readonly IAuthService _authService;
+
+    public AuthController(IAuthService authService)
+    {
+        _authService = authService;
+    }
+
+    [HttpPost("register")]
+    public async Task<ActionResult<AuthResponse>> Register([FromBody] RegisterRequest request)
+    {
+        var result = await _authService.RegisterAsync(request);
+
+        if (result is null)
+            return BadRequest(new { message = "Registrierung fehlgeschlagen. Email existiert bereits oder Passwort ist nicht gültig." });
+
+        return Ok(result);
+    }
+
+    [HttpPost("login")]
+    public async Task<ActionResult<AuthResponse>> Login([FromBody] LoginRequest request)
+    {
+        var result = await _authService.LoginAsync(request);
+
+        if (result is null)
+            return Unauthorized(new { message = "Email oder Passwort falsch." });
+
+        return Ok(result);
+    }
+
+    [Authorize]
+    [HttpGet("me")]
+    public async Task<ActionResult<AuthResponse>> GetCurrentUser()
+    {
+        var userId = User.FindFirstValue(ClaimTypes.NameIdentifier);
+
+        if (userId is null)
+            return Unauthorized();
+
+        var result = await _authService.GetCurrentUserAsync(Guid.Parse(userId));
+
+        if (result is null)
+            return NotFound();
+
+        return Ok(result);
+    }
+}