feat(services): add portrait JPEG normalizer for face enrollment

Adds image normalization (480×640 portrait, JPEG ≤200 KB) required by the ISAPI face upload path. Commit this first so the project builds against the already-committed HikvisionIsapiClient.

src/HikvisionAttendanceManager.App/Services/FaceImageNormalizer.cs

@@ -0,0 +1,109 @@
+using System.Drawing;
+using System.Drawing.Drawing2D;
+using System.Drawing.Imaging;
+using System.IO;
+using System.Runtime.Versioning;
+
+namespace HikvisionAttendanceManager.App.Services;
+
+[SupportedOSPlatform("windows")]
+internal static class FaceImageNormalizer
+{
+    private const int TargetWidth = 480;
+    private const int TargetHeight = 640;
+    private const int MaxBytes = 200 * 1024;
+    private const int MaxQuality = 92;
+    private const int MinQuality = 55;
+
+    public static bool TryNormalizeForEnrollment(byte[] input, out byte[] jpegBytes, out string note)
+    {
+        jpegBytes = [];
+        note = "";
+        if (input.Length < 4 || input[0] != 0xFF || input[1] != 0xD8 || input[2] != 0xFF)
+        {
+            note = "Input is not a JPEG.";
+            return false;
+        }
+
+        try
+        {
+            using var sourceStream = new MemoryStream(input);
+            using var source = Image.FromStream(sourceStream);
+            using var portrait = CropPortrait(source, TargetWidth, TargetHeight);
+            jpegBytes = CompressToTargetSize(portrait);
+            note = $"normalized={TargetWidth}x{TargetHeight} bytes={jpegBytes.Length}";
+            return jpegBytes.Length > 0;
+        }
+        catch (Exception ex)
+        {
+            note = ex.Message;
+            return false;
+        }
+    }
+
+    private static Bitmap CropPortrait(Image source, int targetWidth, int targetHeight)
+    {
+        var targetAspect = (double)targetWidth / targetHeight;
+        var sourceAspect = (double)source.Width / source.Height;
+
+        int cropWidth;
+        int cropHeight;
+        if (sourceAspect > targetAspect)
+        {
+            cropHeight = source.Height;
+            cropWidth = (int)Math.Round(cropHeight * targetAspect);
+        }
+        else
+        {
+            cropWidth = source.Width;
+            cropHeight = (int)Math.Round(cropWidth / targetAspect);
+        }
+
+        var cropX = Math.Max(0, (source.Width - cropWidth) / 2);
+        var cropY = Math.Max(0, (source.Height - cropHeight) / 2);
+        cropWidth = Math.Min(cropWidth, source.Width - cropX);
+        cropHeight = Math.Min(cropHeight, source.Height - cropY);
+
+        var bitmap = new Bitmap(targetWidth, targetHeight);
+        using var graphics = Graphics.FromImage(bitmap);
+        graphics.CompositingQuality = CompositingQuality.HighQuality;
+        graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
+        graphics.SmoothingMode = SmoothingMode.HighQuality;
+        graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;
+        graphics.DrawImage(source,
+            new Rectangle(0, 0, targetWidth, targetHeight),
+            new Rectangle(cropX, cropY, cropWidth, cropHeight),
+            GraphicsUnit.Pixel);
+        return bitmap;
+    }
+
+    private static byte[] CompressToTargetSize(Bitmap bitmap)
+    {
+        byte[]? best = null;
+        for (var quality = MaxQuality; quality >= MinQuality; quality -= 3)
+        {
+            var candidate = SaveJpeg(bitmap, quality);
+            best = candidate;
+            if (candidate.Length <= MaxBytes)
+                return candidate;
+        }
+
+        return best ?? [];
+    }
+
+    private static byte[] SaveJpeg(Image image, int quality)
+    {
+        using var stream = new MemoryStream();
+        using var encoderParameters = new EncoderParameters(1);
+        encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, quality);
+        var codec = ImageCodecInfo.GetImageEncoders().FirstOrDefault(info => info.FormatID == ImageFormat.Jpeg.Guid);
+        if (codec is null)
+        {
+            image.Save(stream, ImageFormat.Jpeg);
+            return stream.ToArray();
+        }
+
+        image.Save(stream, codec, encoderParameters);
+        return stream.ToArray();
+    }
+}