Add Explorer Workbench with hierarchical, off-UI Storage analysis.

Storage queries run in the background with cancellation and covering indexes so switching views no longer freezes the UI.

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

tests/Explorer.Application.Tests/PathHistoryStoreTests.cs

@@ -0,0 +1,49 @@
+using Explorer.Application;
+using Explorer.Domain.Abstractions;
+
+namespace Explorer.Application.Tests;
+
+public class PathHistoryStoreTests
+{
+    [Fact]
+    public void Remember_moves_existing_path_to_front()
+    {
+        var next = PathHistoryStore.Remember(["D:\\Photos", "C:\\"], @"c:\");
+        Assert.Equal(@"c:\", next[0]);
+        Assert.Equal(2, next.Count);
+        Assert.Equal(@"D:\Photos", next[1]);
+    }
+
+    [Fact]
+    public void Load_and_save_roundtrip()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), "ew-path-history", Guid.NewGuid().ToString("N"));
+        try
+        {
+            var store = new PathHistoryStore(new HistoryEnv(dir));
+            store.Save(["C:\\Work", "This PC", "  "]);
+            var loaded = store.Load();
+            Assert.Equal(["C:\\Work"], loaded);
+        }
+        finally
+        {
+            try { Directory.Delete(dir, true); } catch { /* ignore */ }
+        }
+    }
+}
+
+file sealed class HistoryEnv : IAppEnvironment
+{
+    public HistoryEnv(string dir)
+    {
+        DataDirectory = dir;
+        Directory.CreateDirectory(dir);
+        DatabasePath = Path.Combine(dir, "index.db");
+        LogDirectory = Path.Combine(dir, "logs");
+        Directory.CreateDirectory(LogDirectory);
+    }
+
+    public string DataDirectory { get; }
+    public string DatabasePath { get; }
+    public string LogDirectory { get; }
+}