Add JWT authentication and authorization infrastructure

Distribution/Features/Auth/AuthController.cs

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+using Microsoft.AspNetCore.Mvc;
+
+namespace Distribution.Features.Auth;
+
+[ApiController]
+[Route("api/auth")]
+public class AuthController(AuthService service) : ControllerBase
+{
+    [HttpPost("login")]
+    public async Task<IActionResult> Login(LoginRequest request)
+    {
+        var result = await service.LoginAsync(request);
+        return result is null ? Unauthorized() : Ok(result);
+    }
+}

Distribution/Features/Auth/AuthDTOs.cs

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+namespace Distribution.Features.Auth;
+
+public record LoginRequest(string Username, string Password);
+
+public record LoginResponse(string Token, Guid UserId, string Username, string RoleName);

Distribution/Features/Auth/AuthService.cs

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+using Distribution.Features.User;
+using Distribution.Infra.Auth;
+using Microsoft.AspNetCore.Identity;
+
+namespace Distribution.Features.Auth;
+
+public class AuthService(IUserRepository userRepo, IJwtTokenService tokenService)
+{
+    private readonly PasswordHasher<Models.User> _hasher = new();
+
+    public async Task<LoginResponse?> LoginAsync(LoginRequest request)
+    {
+        var user = await userRepo.GetByUsernameAsync(request.Username);
+        if (user is null || !user.IsActive)
+            return null;
+
+        var result = _hasher.VerifyHashedPassword(user, user.PasswordHash, request.Password);
+        if (result == PasswordVerificationResult.Failed)
+            return null;
+
+        var token = tokenService.GenerateToken(user);
+        return new LoginResponse(token, user.Id, user.Username, user.Role?.Name ?? string.Empty);
+    }
+}