Add Git overlay, operation tools, and virtualized preview so large folders stay responsive.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/Explorer.Application.Tests/GitPorcelainParserTests.cs

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+using Explorer.Application;
+using Explorer.Domain;
+
+namespace Explorer.Application.Tests;
+
+public class GitPorcelainParserTests
+{
+    [Fact]
+    public void Parses_branch_counts_and_ahead_behind()
+    {
+        var status = GitPorcelainParser.Parse("""
+            # branch.oid abcdef1234567890
+            # branch.head main
+            # branch.upstream origin/main
+            # branch.ab +2 -1
+            1 .M N... 100644 100644 100644 a a src/App.cs
+            1 M. N... 100644 100644 100644 b b README.md
+            2 R. N... 100644 100644 100644 c c R100 old.txt	new.txt
+            ? bin/out.dll
+            ? notes.md
+            ! ignore.me
+            """, @"C:\src");
+        Assert.NotNull(status);
+        Assert.Equal("main", status.Branch);
+        Assert.Equal(3, status.ModifiedCount);
+        Assert.Equal(2, status.UntrackedCount);
+        Assert.Equal(2, status.Ahead);
+        Assert.Equal(1, status.Behind);
+        Assert.False(status.WorkingTreeClean);
+        Assert.Equal("main · 3 modified · 2 untracked · 2 ahead · 1 behind", status.Badge);
+    }
+
+    [Fact]
+    public void Clean_tree_uses_detached_oid_prefix()
+    {
+        var status = GitPorcelainParser.Parse("""
+            # branch.oid 0123456789abcdef
+            # branch.head (detached)
+            """, @"F:\repo");
+        Assert.NotNull(status);
+        Assert.Equal("0123456", status.Branch);
+        Assert.True(status.WorkingTreeClean);
+        Assert.Equal("0123456 · clean", status.Badge);
+    }
+
+    [Fact]
+    public void Empty_output_is_null()
+        => Assert.Null(GitPorcelainParser.Parse("", @"C:\src"));
+}
+
+public class GitLocatorTests
+{
+    [Fact]
+    public void Prefers_the_configured_path_when_it_exists()
+    {
+        var path = @"C:\Tools\git.exe";
+        Assert.Equal(path, GitLocator.Find(path, fileExists: p => p == path, pathVariable: ""));
+    }
+
+    [Fact]
+    public void Finds_git_on_PATH()
+    {
+        var found = GitLocator.Find(
+            null,
+            fileExists: p => p.Equals(@"D:\bin\git.exe", StringComparison.OrdinalIgnoreCase),
+            pathVariable: @"C:\Windows;D:\bin");
+        Assert.Equal(@"D:\bin\git.exe", found);
+    }
+
+    [Fact]
+    public void Returns_null_when_git_is_missing()
+        => Assert.Null(GitLocator.Find(null, fileExists: _ => false, pathVariable: @"C:\none"));
+}
+
+public class GitRepoDetectorTests
+{
+    [Fact]
+    public void Finds_the_repo_root_from_a_nested_path()
+    {
+        var dirs = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { @"C:\src", @"C:\src\.git", @"C:\src\app" };
+        var files = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+        Assert.Equal(@"C:\src", GitRepoDetector.FindRoot(@"C:\src\app\Main.cs", dirs.Contains, files.Contains));
+        Assert.True(GitRepoDetector.IsRepoRoot(@"C:\src", dirs.Contains, files.Contains));
+        Assert.False(GitRepoDetector.IsRepoRoot(@"C:\src\app", dirs.Contains, files.Contains));
+    }
+
+    [Fact]
+    public void Treats_a_gitfile_as_a_worktree_root()
+    {
+        var dirs = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { @"C:\work" };
+        var files = new HashSet<string>(StringComparer.OrdinalIgnoreCase) { @"C:\work\.git" };
+        Assert.Equal(@"C:\work", GitRepoDetector.FindRoot(@"C:\work", dirs.Contains, files.Contains));
+    }
+
+    [Fact]
+    public void Virtual_roots_are_not_repos()
+        => Assert.Null(GitRepoDetector.FindRoot(LocationRoots.ThisPc, _ => true, _ => true));
+}