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

tests/Paca.Tests/Platform/AvaloniaShellGateTests.cs

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+using System.IO;
+using System.Text.RegularExpressions;
+using Xunit;
+
+namespace Paca.Tests.Platform;
+
+/// <summary>
+/// Avalonia 크로스플랫폼 셸 회귀 방지 게이트 테스트 (Phase 5).
+/// AVLN5001 경고 회귀 방어, MVVM 데이터 바인딩 무결성, URL 분류 로직 검증.
+/// </summary>
+public class AvaloniaShellGateTests
+{
+    private static string GetSolutionRoot()
+    {
+        var dir = AppContext.BaseDirectory;
+        while (!string.IsNullOrEmpty(dir) && !File.Exists(Path.Combine(dir, "Paca.slnx")) && !File.Exists(Path.Combine(dir, "Paca.sln")))
+        {
+            var parent = Directory.GetParent(dir);
+            if (parent == null) break;
+            dir = parent.FullName;
+        }
+        return dir ?? AppContext.BaseDirectory;
+    }
+
+    private static string AvaloniaProjectDir => Path.Combine(GetSolutionRoot(), "src", "Paca.Avalonia");
+
+    [Fact]
+    public void Gate_MainWindow_Axaml_Complies_With_Modern_Avalonia_Standards()
+    {
+        var axamlPath = Path.Combine(AvaloniaProjectDir, "MainWindow.axaml");
+        Assert.True(File.Exists(axamlPath), $"MainWindow.axaml must exist at {axamlPath}");
+
+        var axamlContent = File.ReadAllText(axamlPath);
+
+        // AVLN5001 방어: Obsolete Watermark 속성 사용 금지
+        Assert.DoesNotContain("Watermark=", axamlContent);
+
+        // PlaceholderText 속성 사용 확인
+        Assert.Contains("PlaceholderText=", axamlContent);
+
+        // 핵심 MVVM 바인딩 요소 존재 검증
+        Assert.Contains("{Binding Url", axamlContent);
+        Assert.Contains("{Binding Status", axamlContent);
+        Assert.Contains("{Binding Progress", axamlContent);
+        Assert.Contains("{Binding DownloadCommand}", axamlContent);
+        Assert.Contains("{Binding CancelCommand}", axamlContent);
+    }
+
+    [Fact]
+    public void Gate_MainViewModel_Contains_All_Required_Contracts()
+    {
+        var vmPath = Path.Combine(AvaloniaProjectDir, "MainViewModel.cs");
+        Assert.True(File.Exists(vmPath), $"MainViewModel.cs must exist at {vmPath}");
+
+        var vmContent = File.ReadAllText(vmPath);
+
+        // INotifyPropertyChanged 구현 및 RelayCommand 검증
+        Assert.Contains("INotifyPropertyChanged", vmContent);
+        Assert.Contains("RelayCommand", vmContent);
+        Assert.Contains("DownloadCommand", vmContent);
+        Assert.Contains("CancelCommand", vmContent);
+        Assert.Contains("DownloadByKindAsync", vmContent);
+        Assert.Contains("Classify", vmContent);
+
+        // 4대 스트림 타입 분기 검증
+        Assert.Contains("Kind.Social", vmContent);
+        Assert.Contains("Kind.Hls", vmContent);
+        Assert.Contains("Kind.Dash", vmContent);
+        Assert.Contains("Kind.Direct", vmContent);
+    }
+
+    [Theory]
+    [InlineData("https://www.youtube.com/watch?v=dQw4w9WgXcQ", "Social")]
+    [InlineData("https://youtu.be/dQw4w9WgXcQ", "Social")]
+    [InlineData("https://instagram.com/reel/123456", "Social")]
+    [InlineData("https://tiktok.com/@user/video/12345", "Social")]
+    [InlineData("https://x.com/user/status/12345", "Social")]
+    [InlineData("https://twitter.com/user/status/12345", "Social")]
+    [InlineData("https://example.com/video/master.m3u8", "Hls")]
+    [InlineData("https://example.com/stream/manifest.mpd", "Dash")]
+    [InlineData("https://example.com/files/video.mp4", "Direct")]
+    public void Gate_Url_Classification_Matches_Expected_Kind(string rawUrl, string expectedKind)
+    {
+        var uri = new Uri(rawUrl);
+        var actualKind = Paca.Avalonia.MainViewModel.Classify(uri).ToString();
+
+        Assert.Equal(expectedKind, actualKind);
+    }
+}