feat(app): implement RefreshCommand handler with token rotation and chain revocation

src/api/SIGCM2.Application/Auth/Refresh/RefreshCommand.cs

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+namespace SIGCM2.Application.Auth.Refresh;
+
+public sealed record RefreshCommand(string AccessToken, string RefreshToken);

src/api/SIGCM2.Application/Auth/Refresh/RefreshCommandHandler.cs

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+using SIGCM2.Application.Abstractions;
+using SIGCM2.Application.Abstractions.Persistence;
+using SIGCM2.Application.Abstractions.Security;
+using SIGCM2.Domain.Entities;
+using SIGCM2.Domain.Exceptions;
+using SIGCM2.Domain.Security;
+
+namespace SIGCM2.Application.Auth.Refresh;
+
+public sealed class RefreshCommandHandler : ICommandHandler<RefreshCommand, RefreshResponseDto>
+{
+    private readonly IRefreshTokenRepository _refreshRepo;
+    private readonly IUsuarioRepository _usuarioRepo;
+    private readonly IJwtService _jwt;
+    private readonly IRefreshTokenGenerator _refreshGenerator;
+    private readonly IClientContext _clientCtx;
+    private readonly AuthOptions _authOptions;
+
+    public RefreshCommandHandler(
+        IRefreshTokenRepository refreshRepo,
+        IUsuarioRepository usuarioRepo,
+        IJwtService jwt,
+        IRefreshTokenGenerator refreshGenerator,
+        IClientContext clientCtx,
+        AuthOptions authOptions)
+    {
+        _refreshRepo = refreshRepo;
+        _usuarioRepo = usuarioRepo;
+        _jwt = jwt;
+        _refreshGenerator = refreshGenerator;
+        _clientCtx = clientCtx;
+        _authOptions = authOptions;
+    }
+
+    public async Task<RefreshResponseDto> Handle(RefreshCommand command)
+    {
+        // 1. Validate access token signature (lifetime=false) and extract sub
+        System.Security.Claims.ClaimsPrincipal principal;
+        try
+        {
+            principal = _jwt.GetPrincipalFromExpiredToken(command.AccessToken);
+        }
+        catch
+        {
+            throw new InvalidRefreshTokenException();
+        }
+
+        if (!int.TryParse(principal.FindFirst("sub")?.Value, out var accessUserId))
+            throw new InvalidRefreshTokenException();
+
+        // 2. Hash the refresh token to look it up
+        var hash = TokenHasher.Sha256Base64Url(command.RefreshToken);
+
+        // 3. Look up in DB (returns record regardless of revoked/expired status)
+        var stored = await _refreshRepo.GetByHashAsync(hash);
+        if (stored is null)
+            throw new InvalidRefreshTokenException();
+
+        var now = DateTime.UtcNow;
+
+        // 4. Reuse detection: already revoked → chain revocation and throw
+        if (stored.IsRevoked)
+        {
+            await _refreshRepo.RevokeFamilyAsync(stored.FamilyId, now);
+            throw new TokenReuseDetectedException();
+        }
+
+        // 5. Absolute expiration check
+        if (stored.IsExpired(now))
+            throw new InvalidRefreshTokenException();
+
+        // 6. UsuarioId must match access token's sub claim
+        if (stored.UsuarioId != accessUserId)
+            throw new InvalidRefreshTokenException();
+
+        // 7. Load current user (so access token has up-to-date claims)
+        var usuario = await _usuarioRepo.GetByIdAsync(stored.UsuarioId)
+                      ?? throw new InvalidRefreshTokenException();
+
+        if (!usuario.Activo)
+            throw new InvalidRefreshTokenException();
+
+        // 8. Rotate: create new token, persist, then revoke old
+        var newRaw = _refreshGenerator.Generate();
+        var newHash = TokenHasher.Sha256Base64Url(newRaw);
+        var rotated = RefreshToken.IssueRotation(stored, newHash, now, _clientCtx.Ip, _clientCtx.UserAgent);
+
+        var newId = await _refreshRepo.AddAsync(rotated);
+        await _refreshRepo.RevokeAsync(stored.Id, replacedById: newId, revokedAt: now);
+
+        // 9. Issue new access token
+        var newAccess = _jwt.GenerateAccessToken(usuario);
+        return new RefreshResponseDto(newAccess, newRaw, _authOptions.AccessTokenMinutes * 60);
+    }
+}

src/api/SIGCM2.Application/Auth/Refresh/RefreshCommandValidator.cs

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+using FluentValidation;
+
+namespace SIGCM2.Application.Auth.Refresh;
+
+public sealed class RefreshCommandValidator : AbstractValidator<RefreshCommand>
+{
+    public RefreshCommandValidator()
+    {
+        RuleFor(x => x.AccessToken)
+            .NotEmpty().WithMessage("accessToken is required");
+
+        RuleFor(x => x.RefreshToken)
+            .NotEmpty().WithMessage("refreshToken is required")
+            .MinimumLength(20).WithMessage("refreshToken must be at least 20 characters");
+    }
+}

src/api/SIGCM2.Application/Auth/Refresh/RefreshResponseDto.cs

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+namespace SIGCM2.Application.Auth.Refresh;
+
+public sealed record RefreshResponseDto(
+    string AccessToken,
+    string RefreshToken,
+    int ExpiresIn);