feat(ads/seo/release): v1.2.0 with live Google Ads, isolated ad profile, ads.txt, and SEO/AEO/GEO optimization

tests/Paca.Tests/Core/AudioChannelDownmixerGateTests.cs

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+using System;
+using Paca.Core;
+using Xunit;
+
+namespace Paca.Tests.Core;
+
+public class AudioChannelDownmixerGateTests
+{
+    [Fact]
+    public void Gate329_AudioChannelDownmixer_BuildsStandardItuR775Filter()
+    {
+        var filter = AudioChannelDownmixer.BuildDownmixFilterArgs(DownmixMode.StandardItuR775);
+
+        Assert.Contains("pan=stereo|FL=0.7071*FL+0.5*FC+0.7071*BL|FR=0.7071*FR+0.5*FC+0.7071*BR", filter);
+    }
+
+    [Fact]
+    public void Gate330_AudioChannelDownmixer_BuildsNightDialogBoostFilter()
+    {
+        var filter = AudioChannelDownmixer.BuildDownmixFilterArgs(DownmixMode.NightDialogBoost);
+
+        // Center channel (FC) boosted to 1.0, side noise attenuated
+        Assert.Contains("pan=stereo|FL=0.5*FL+1.0*FC+0.3*BL|FR=0.5*FR+1.0*FC+0.3*BR", filter);
+    }
+
+    [Fact]
+    public void Gate331_AudioChannelDownmixer_BuildsMonoCompatibilityFilter()
+    {
+        var filter = AudioChannelDownmixer.BuildDownmixFilterArgs(DownmixMode.MonoCompatibility);
+
+        Assert.Contains("pan=mono|c0=0.5*FL+0.5*FR", filter);
+    }
+
+    [Fact]
+    public void Gate332_AudioChannelDownmixer_BuildsFullCommandLine_WithVideoCopy()
+    {
+        var cmd = AudioChannelDownmixer.BuildDownmixCommandLine(
+            inputPath: "C:\\movies\\surround51.mp4",
+            outputPath: "C:\\movies\\stereo_dialog.mp4",
+            mode: DownmixMode.NightDialogBoost,
+            copyVideo: true
+        );
+
+        Assert.Contains("-i \"C:\\movies\\surround51.mp4\"", cmd);
+        Assert.Contains("-c:v copy", cmd);
+        Assert.Contains("-filter:a \"pan=stereo|FL=0.5*FL+1.0*FC+0.3*BL|FR=0.5*FR+1.0*FC+0.3*BR\"", cmd);
+        Assert.Contains("-c:a aac -b:a 192k", cmd);
+        Assert.EndsWith("\"C:\\movies\\stereo_dialog.mp4\" -y", cmd);
+    }
+}