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

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

tests/Explorer.Storage.Tests/SqliteDatabaseSessionTests.cs

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+using Explorer.Application;
+using Explorer.Storage.Sqlite;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace Explorer.Storage.Tests;
+
+public class SqliteDatabaseSessionTests
+{
+    [Fact]
+    public async Task Can_browse_and_edit_a_standalone_database()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), "ew-sql", Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(dir);
+        var path = Path.Combine(dir, "sample.db");
+        var indexPath = Path.Combine(dir, "index.db");
+        await using var writer = new SqliteIndexStore(indexPath, NullLogger<SqliteIndexStore>.Instance);
+        await writer.OpenAsync();
+        await writer.CloseAsync();
+
+        await using var session = new SqliteDatabaseSession(indexPath);
+        await session.OpenAsync(path, preferWrite: true);
+        Assert.True(session.CanWrite);
+        await session.ExecuteAsync("CREATE TABLE notes (id INTEGER PRIMARY KEY, body TEXT);");
+        await session.InsertRowAsync("notes", new Dictionary<string, object?> { ["body"] = "hello" });
+        var page = await session.ReadTableAsync("notes", 0, 50);
+        Assert.Contains("body", page.Columns);
+        Assert.Single(page.Rows);
+        var rowId = Convert.ToInt64(page.Rows[0][0]);
+        await session.UpdateCellAsync("notes", rowId, "body", "world");
+        var query = await session.ExecuteAsync("SELECT body FROM notes");
+        Assert.Equal("world", query.Rows[0][0]?.ToString());
+        await session.DeleteRowAsync("notes", rowId);
+        Assert.Equal(0, (await session.ReadTableAsync("notes", 0, 10)).TotalRows);
+    }
+
+    [Fact]
+    public async Task Index_opens_read_only_while_writer_holds_lock()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), "ew-sql", Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(dir);
+        var path = Path.Combine(dir, "index.db");
+        await using var writer = new SqliteIndexStore(path, NullLogger<SqliteIndexStore>.Instance);
+        await writer.OpenAsync();
+        await using var session = new SqliteDatabaseSession(path);
+        await session.OpenAsync(path, preferWrite: true);
+        Assert.False(session.CanWrite);
+        Assert.Contains("Read-only", session.ModeLabel, StringComparison.OrdinalIgnoreCase);
+        var tables = await session.ListTablesAsync();
+        Assert.Contains("sources", tables);
+    }
+}