Implement ImageCreatorImageSharp using SixLabors.ImageSharp for image processing

- Added ImageCreatorImageSharp class for image creation, handling EXIF orientation, resizing, and saving images.
- Replaced GDI+ dependencies with ImageSharp for cross-platform compatibility.
- Introduced methods for drawing text and logos on images, including handling transparency and positioning.
- Created a test plan for validating ImageCreatorImageSharp functionality, focusing on image resizing, text positioning, logo features, and EXIF orientation.
- Added documentation for the test plan outlining goals, project structure, and implementation notes.

MaddoShared.ImageSharpTests/Tests/TextPositioningTests.cs

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+using System.IO;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using SixLabors.ImageSharp.PixelFormats;
+using MaddoShared.ImageSharpTests.Helpers;
+
+namespace MaddoShared.ImageSharpTests.Tests
+{
+    [TestClass]
+    public class TextPositioningTests
+    {
+        [TestMethod]
+        public async Task TextAtBottom_IncreasesNonBackgroundPixelCountInBottomBand()
+        {
+            using var ws = new TempWorkspace();
+
+            // create white background input
+            var inputPath = TestImageFactory.CreateSolidJpeg(ws.SourceDir.FullName, "input.jpg", 800, 600, new Rgba32(255, 255, 255, 255));
+
+            var pic = CreatorFactory.CreateDefaultPicSettings();
+            pic.Posizione = "BASSO";
+            pic.DimStandard = 48; // big text
+            pic.TestoFirmaStart = "SAMPLE TEXT";
+            pic.CreaMiniature = false;
+
+            var svc = CreatorFactory.CreateImageCreator(pic);
+
+            var state = new MaddoShared.ImageState
+            {
+                WorkFile = new FileInfo(inputPath),
+                DestDir = ws.DestDir,
+                SourceDir = ws.SourceDir
+            };
+
+            await svc.CreateImageAsync(state, null);
+
+            var outPath = Path.Combine(ws.DestDir.FullName, state.NomeFileBig);
+
+            // bottom band (lower 25% of image)
+            var bottomY = (int)(600 * 0.75);
+            var bottomCount = PixelInspector.CountNonBackgroundPixels(outPath, 0, bottomY, 800, 600 - bottomY, new Rgba32(255, 255, 255, 255), tolerance: 10);
+
+            // top band (upper 25%)
+            var topCount = PixelInspector.CountNonBackgroundPixels(outPath, 0, 0, 800, (int)(600 * 0.25), new Rgba32(255, 255, 255, 255), tolerance: 10);
+
+            Assert.IsTrue(bottomCount > 50, $"Expected text pixels in bottom band, found {bottomCount}");
+            Assert.IsTrue(bottomCount > topCount, "Expected more non-background pixels at bottom than top");
+        }
+    }
+}