feat(ui): add RepoScanner for git repo discovery

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

tests/ClaudeDo.Ui.Tests/RepoScannerTests.cs

@@ -0,0 +1,78 @@
+using ClaudeDo.Ui.Services;
+
+namespace ClaudeDo.Ui.Tests;
+
+public sealed class RepoScannerTests : IDisposable
+{
+    private readonly string _root =
+        Path.Combine(Path.GetTempPath(), "repo-scan-" + Guid.NewGuid().ToString("N"));
+
+    public RepoScannerTests() => Directory.CreateDirectory(_root);
+
+    public void Dispose()
+    {
+        try { Directory.Delete(_root, recursive: true); } catch { }
+    }
+
+    private string MakeDir(string name)
+    {
+        var p = Path.Combine(_root, name);
+        Directory.CreateDirectory(p);
+        return p;
+    }
+
+    [Fact]
+    public void Scan_ReturnsSubfoldersWithGitDirectory()
+    {
+        var repo = MakeDir("repo-a");
+        Directory.CreateDirectory(Path.Combine(repo, ".git"));
+
+        var result = RepoScanner.Scan(_root);
+
+        Assert.Single(result);
+        Assert.Equal("repo-a", result[0].Name);
+        Assert.Equal(repo, result[0].FullPath);
+    }
+
+    [Fact]
+    public void Scan_TreatsDotGitFileAsRepo()
+    {
+        var repo = MakeDir("worktree-repo");
+        File.WriteAllText(Path.Combine(repo, ".git"), "gitdir: ../somewhere");
+
+        var result = RepoScanner.Scan(_root);
+
+        Assert.Single(result);
+        Assert.Equal("worktree-repo", result[0].Name);
+    }
+
+    [Fact]
+    public void Scan_IgnoresPlainFolders()
+    {
+        MakeDir("not-a-repo");
+
+        var result = RepoScanner.Scan(_root);
+
+        Assert.Empty(result);
+    }
+
+    [Fact]
+    public void Scan_IsNotRecursive()
+    {
+        var nested = MakeDir(Path.Combine("outer", "inner"));
+        Directory.CreateDirectory(Path.Combine(nested, ".git"));
+        // outer itself has no .git
+
+        var result = RepoScanner.Scan(_root);
+
+        Assert.Empty(result);
+    }
+
+    [Fact]
+    public void Scan_ReturnsEmptyForMissingFolder()
+    {
+        var result = RepoScanner.Scan(Path.Combine(_root, "does-not-exist"));
+
+        Assert.Empty(result);
+    }
+}