Merge branch 'feat/self-update'

Self-update for app and installer. Integrates cleanly with the
worker-log-footer feature that landed on main in parallel — the
shell VM now carries both worker-log state and update-check state,
and MainWindow hosts both the update banner and the footer log line.

Conflict resolved in IslandsShellViewModel.cs: kept nullable property
types from main's test-only parameterless constructor work, and added
the UpdateCheck property exposing the injected service.

tests/ClaudeDo.Ui.Tests/Services/InstallerLocatorTests.cs

@@ -0,0 +1,58 @@
+using ClaudeDo.Ui.Services;
+
+namespace ClaudeDo.Ui.Tests.Services;
+
+public class InstallerLocatorTests : IDisposable
+{
+    private readonly string _root;
+
+    public InstallerLocatorTests()
+    {
+        _root = Path.Combine(Path.GetTempPath(), "ClaudeDo.Ui.Tests-" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(_root);
+    }
+
+    public void Dispose() { try { Directory.Delete(_root, true); } catch { } }
+
+    [Fact]
+    public void Find_WalkUpFromAppDir_ToInstallJsonSibling()
+    {
+        var installDir = Path.Combine(_root, "ClaudeDo");
+        var appDir = Path.Combine(installDir, "app");
+        var uninstallerDir = Path.Combine(installDir, "uninstaller");
+        Directory.CreateDirectory(appDir);
+        Directory.CreateDirectory(uninstallerDir);
+
+        File.WriteAllText(Path.Combine(installDir, "install.json"), "{}");
+        var installerPath = Path.Combine(uninstallerDir, "ClaudeDo.Installer.exe");
+        File.WriteAllText(installerPath, "x");
+
+        var locator = new InstallerLocator();
+        var found = locator.FindByWalkingUp(appDir);
+
+        Assert.Equal(installerPath, found);
+    }
+
+    [Fact]
+    public void Find_ReturnsNullWhenNoInstallJson()
+    {
+        var appDir = Path.Combine(_root, "somewhere", "app");
+        Directory.CreateDirectory(appDir);
+
+        var locator = new InstallerLocator();
+        Assert.Null(locator.FindByWalkingUp(appDir));
+    }
+
+    [Fact]
+    public void Find_ReturnsNullWhenInstallerMissingFromUninstallerDir()
+    {
+        var installDir = Path.Combine(_root, "ClaudeDo");
+        var appDir = Path.Combine(installDir, "app");
+        Directory.CreateDirectory(appDir);
+        Directory.CreateDirectory(Path.Combine(installDir, "uninstaller"));
+        File.WriteAllText(Path.Combine(installDir, "install.json"), "{}");
+
+        var locator = new InstallerLocator();
+        Assert.Null(locator.FindByWalkingUp(appDir));
+    }
+}

tests/ClaudeDo.Ui.Tests/Services/UpdateCheckServiceTests.cs

@@ -0,0 +1,62 @@
+using System.Net.Http;
+using ClaudeDo.Releases;
+using ClaudeDo.Ui.Services;
+
+namespace ClaudeDo.Ui.Tests.Services;
+
+public class UpdateCheckServiceTests
+{
+    private sealed class FakeReleaseClient : IReleaseClient
+    {
+        public GiteaRelease? Release { get; set; }
+        public bool Throw { get; set; }
+
+        public Task<GiteaRelease?> GetLatestReleaseAsync(CancellationToken ct)
+        {
+            if (Throw) throw new HttpRequestException();
+            return Task.FromResult(Release);
+        }
+
+        public Task DownloadAsync(string url, string destPath, IProgress<long> progress, CancellationToken ct)
+            => throw new NotSupportedException();
+    }
+
+    [Fact]
+    public async Task Check_NewerRelease_SetsUpdateAvailable()
+    {
+        var svc = new UpdateCheckService(new FakeReleaseClient
+        {
+            Release = new GiteaRelease("v0.3.0", "r", new[] { new ReleaseAsset("ClaudeDo-0.3.0-win-x64.zip", "u", 1) }),
+        },
+        currentVersion: "0.1.0");
+
+        await svc.CheckNowAsync(CancellationToken.None);
+
+        Assert.Equal(UpdateCheckStatus.UpdateAvailable, svc.LastCheckStatus);
+        Assert.True(svc.IsUpdateAvailable);
+        Assert.Equal("0.3.0", svc.LatestVersion);
+    }
+
+    [Fact]
+    public async Task Check_SameRelease_SetsUpToDate()
+    {
+        var svc = new UpdateCheckService(new FakeReleaseClient
+        {
+            Release = new GiteaRelease("v0.1.0", "r", new[] { new ReleaseAsset("ClaudeDo-0.1.0-win-x64.zip", "u", 1) }),
+        },
+        currentVersion: "0.1.0");
+
+        await svc.CheckNowAsync(CancellationToken.None);
+
+        Assert.Equal(UpdateCheckStatus.UpToDate, svc.LastCheckStatus);
+        Assert.False(svc.IsUpdateAvailable);
+    }
+
+    [Fact]
+    public async Task Check_NetworkError_SetsCheckFailedButDoesNotThrow()
+    {
+        var svc = new UpdateCheckService(new FakeReleaseClient { Throw = true }, "0.1.0");
+        await svc.CheckNowAsync(CancellationToken.None);
+        Assert.Equal(UpdateCheckStatus.CheckFailed, svc.LastCheckStatus);
+    }
+}