feat(installer): replace sync ModeDetector with async InstallModeDetector

Placeholder edit to App.xaml.cs to keep the project building until Task 11
wires the new async detector.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/ClaudeDo.Installer.Tests/InstallModeDetectorTests.cs

@@ -0,0 +1,105 @@
+using ClaudeDo.Installer.Core;
+
+namespace ClaudeDo.Installer.Tests;
+
+public sealed class InstallModeDetectorTests : IDisposable
+{
+    private readonly string _tempDir;
+
+    public InstallModeDetectorTests()
+    {
+        _tempDir = Path.Combine(Path.GetTempPath(), "ClaudeDoDetector-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(_tempDir);
+    }
+
+    public void Dispose()
+    {
+        try { Directory.Delete(_tempDir, recursive: true); } catch { }
+    }
+
+    private sealed class FakeReleaseClient : IReleaseClient
+    {
+        public GiteaRelease? Release { get; set; }
+        public Task<GiteaRelease?> GetLatestReleaseAsync(CancellationToken ct) => Task.FromResult(Release);
+        public Task DownloadAsync(string url, string destPath, IProgress<long> progress, CancellationToken ct)
+            => throw new NotSupportedException();
+    }
+
+    [Fact]
+    public async Task Detect_FreshInstall_WhenManifestMissing()
+    {
+        var detector = new InstallModeDetector(new FakeReleaseClient());
+
+        var state = await detector.DetectAsync(_tempDir, CancellationToken.None);
+
+        Assert.Equal(InstallerMode.FreshInstall, state.Mode);
+        Assert.Null(state.Existing);
+    }
+
+    [Fact]
+    public async Task Detect_Config_WhenManifestPresent_And_Api_Unreachable()
+    {
+        InstallManifestStore.Write(_tempDir,
+            new InstallManifest("0.1.0", _tempDir, _tempDir, DateTimeOffset.UtcNow));
+
+        var detector = new InstallModeDetector(new FakeReleaseClient { Release = null });
+
+        var state = await detector.DetectAsync(_tempDir, CancellationToken.None);
+
+        Assert.Equal(InstallerMode.Config, state.Mode);
+        Assert.Equal("0.1.0", state.Existing!.Version);
+    }
+
+    [Fact]
+    public async Task Detect_Update_WhenLatest_GreaterThan_Installed()
+    {
+        InstallManifestStore.Write(_tempDir,
+            new InstallManifest("0.1.0", _tempDir, _tempDir, DateTimeOffset.UtcNow));
+
+        var fake = new FakeReleaseClient
+        {
+            Release = new GiteaRelease("v0.2.0", "v0.2.0", Array.Empty<ReleaseAsset>())
+        };
+        var detector = new InstallModeDetector(fake);
+
+        var state = await detector.DetectAsync(_tempDir, CancellationToken.None);
+
+        Assert.Equal(InstallerMode.Update, state.Mode);
+        Assert.Equal("0.1.0", state.Existing!.Version);
+        Assert.Equal("0.2.0", state.LatestVersion);
+    }
+
+    [Fact]
+    public async Task Detect_Config_WhenLatest_EqualsOrOlderThan_Installed()
+    {
+        InstallManifestStore.Write(_tempDir,
+            new InstallManifest("0.2.0", _tempDir, _tempDir, DateTimeOffset.UtcNow));
+
+        var fake = new FakeReleaseClient
+        {
+            Release = new GiteaRelease("v0.2.0", "v0.2.0", Array.Empty<ReleaseAsset>())
+        };
+        var detector = new InstallModeDetector(fake);
+
+        var state = await detector.DetectAsync(_tempDir, CancellationToken.None);
+
+        Assert.Equal(InstallerMode.Config, state.Mode);
+    }
+
+    [Fact]
+    public async Task Detect_Config_WhenInstalledIs_Newer_Than_Latest()
+    {
+        InstallManifestStore.Write(_tempDir,
+            new InstallManifest("0.3.0", _tempDir, _tempDir, DateTimeOffset.UtcNow));
+
+        var fake = new FakeReleaseClient
+        {
+            Release = new GiteaRelease("v0.2.0", "v0.2.0", Array.Empty<ReleaseAsset>())
+        };
+        var detector = new InstallModeDetector(fake);
+
+        var state = await detector.DetectAsync(_tempDir, CancellationToken.None);
+
+        Assert.Equal(InstallerMode.Config, state.Mode);
+    }
+}