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.Worker/Program.cs

@@ -1,3 +1,4 @@
+using System.Threading;
 using ClaudeDo.Data;
 using ClaudeDo.Data.Git;
 using ClaudeDo.Data.Repositories;
@@ -13,14 +14,28 @@ using ClaudeDo.Worker.State;
 using ClaudeDo.Worker.Prime;
 using ClaudeDo.Worker.Worktrees;
 using Microsoft.EntityFrameworkCore;
+using Serilog;
+
+// Single-instance per user session. Multiple launch paths exist (logon task,
+// app ensure-running, Restart button); a second instance exits cleanly instead
+// of fighting over the SignalR port.
+var mutex = new Mutex(true, @"Local\ClaudeDoWorker", out var createdNew);
+if (!createdNew)
+    return; // another instance already owns the port; exit 0
 
 var cfg = WorkerConfig.Load();
 
 var builder = WebApplication.CreateBuilder(args);
 
-// When launched by the Windows SCM, speak the Service Control Protocol so SCM
-// doesn't think we crashed (~30s timeout). No-op when running interactively.
-builder.Host.UseWindowsService(o => o.ServiceName = "ClaudeDoWorker");
+var logRoot = cfg.LogRoot;
+Directory.CreateDirectory(logRoot);
+builder.Host.UseSerilog((ctx, lc) => lc
+    .MinimumLevel.Information()
+    .WriteTo.File(
+        System.IO.Path.Combine(logRoot, "worker-.log"),
+        rollingInterval: RollingInterval.Day,
+        retainedFileCountLimit: 7,
+        shared: true));
 
 builder.Services.AddDbContextFactory<ClaudeDoDbContext>(opt =>
     opt.UseSqlite($"Data Source={cfg.DbPath}"));
@@ -209,3 +224,5 @@ else
 {
     await Task.WhenAll(app.RunAsync(), externalApp.RunAsync());
 }
+
+GC.KeepAlive(mutex);