Add video preview, source crop, find-videos, and render toasts

Bring the Video tab closer to Shorts with 4K preview stills and crop
modes (none, auto, center, plus the visual editor). Settings store a
default source folder so Find videos can collect output.avi sequences.
Cap the FFmpeg log with auto-scroll, hide repeat spam, and show a
Windows notification when a video or short finishes or fails.

AmiReel.Tests/Services/ProcessRunnerTests.cs

@@ -0,0 +1,34 @@
+using AmiReel.Services;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace AmiReel.Tests.Services;
+
+[TestClass]
+public class ProcessRunnerTests
+{
+    [TestMethod]
+    public void IsNoise_WithLastMessageRepeated_ReturnsTrue()
+    {
+        // Arrange
+        FfmpegOutputLine line = FfmpegProgressParser.Parse("Last message repeated 1 times");
+
+        // Act
+        bool result = ProcessRunner.IsNoise(line);
+
+        // Assert
+        Assert.IsTrue(result);
+    }
+
+    [TestMethod]
+    public void IsNoise_WithCropdetectSpec_ReturnsFalse()
+    {
+        // Arrange
+        FfmpegOutputLine line = FfmpegProgressParser.Parse("crop=672:ih:56:0");
+
+        // Act
+        bool result = ProcessRunner.IsNoise(line);
+
+        // Assert
+        Assert.IsFalse(result);
+    }
+}