feat(worker): run worker as per-user logon task instead of Windows service

A LocalSystem Windows service can't see the logged-in user's Claude CLI
authentication, so the worker now runs as the current user via a hidden
per-user logon Scheduled Task with restart-on-failure.

- Worker is WinExe (no console window) with a Serilog rolling file sink and
  a single-instance mutex so the logon task, app ensure-running, and Restart
  button can't fight over the SignalR port.
- Installer replaces the service steps (register/start/stop) with autostart
  task steps, migrates the legacy ClaudeDoWorker service away on update, and
  removes the task on uninstall. ServicePage drops the service-account UI.
- UI gains a WorkerLocator; the app ensures the worker is running at startup
  and the Restart button kills+relaunches this install's worker process.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/ClaudeDo.Installer/Steps/StopWorkerStep.cs

@@ -0,0 +1,48 @@
+using System.Diagnostics;
+using System.IO;
+using ClaudeDo.Installer.Core;
+
+namespace ClaudeDo.Installer.Steps;
+
+public sealed class StopWorkerStep : IInstallStep
+{
+    public const string TaskName = "ClaudeDoWorker";
+    public const string ProcessName = "ClaudeDo.Worker";
+
+    public string Name => "Stop Worker";
+
+    public async Task<StepResult> ExecuteAsync(InstallContext ctx, IProgress<string> progress, CancellationToken ct)
+    {
+        progress.Report("Stopping worker task (if running)...");
+        await ProcessRunner.RunAsync("schtasks.exe", $"/End /TN \"{TaskName}\"", null, progress, ct);
+
+        progress.Report("Stopping worker process (if running)...");
+        var installDir = ctx.InstallDirectory;
+        foreach (var p in Process.GetProcessesByName(ProcessName))
+        {
+            try
+            {
+                var path = p.MainModule?.FileName;
+                if (path is not null && !IsUnder(path, installDir)) continue;
+                p.Kill(entireProcessTree: true);
+                p.WaitForExit(10000);
+            }
+            catch { /* process may have exited or be inaccessible */ }
+            finally { p.Dispose(); }
+        }
+        await Task.CompletedTask;
+        return StepResult.Ok();
+    }
+
+    private static bool IsUnder(string filePath, string dir)
+    {
+        try
+        {
+            if (string.IsNullOrWhiteSpace(dir)) return true; // can't scope — be permissive
+            var full = Path.GetFullPath(filePath);
+            var root = Path.GetFullPath(dir).TrimEnd(Path.DirectorySeparatorChar) + Path.DirectorySeparatorChar;
+            return full.StartsWith(root, StringComparison.OrdinalIgnoreCase);
+        }
+        catch { return false; }
+    }
+}