Add host activity and DB browser, and keep dialogs, drag-drop, and idle maintenance responsive.

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

tests/Explorer.Application.Tests/HostActivityLogTests.cs

@@ -0,0 +1,31 @@
+using Explorer.Application;
+using Explorer.Contracts;
+
+namespace Explorer.Application.Tests;
+
+public class HostActivityLogTests
+{
+    [Fact]
+    public void Ring_keeps_recent_events_in_order()
+    {
+        var log = new HostActivityLog(8);
+        for (var i = 0; i < 10; i++)
+        {
+            log.Record("Indexing", "file-" + i);
+        }
+
+        var recent = log.TakeRecent(5);
+        Assert.Equal(5, recent.Count);
+        Assert.Equal("file-5", recent[0].Message);
+        Assert.Equal("file-9", recent[^1].Message);
+    }
+
+    [Fact]
+    public void Duplicate_messages_are_coalesced()
+    {
+        var log = new HostActivityLog();
+        log.Record("Maintenance", "same");
+        log.Record("Maintenance", "same");
+        Assert.Single(log.TakeRecent());
+    }
+}