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/Core/ScheduledTaskXml.cs

@@ -0,0 +1,52 @@
+using System.Security;
+
+namespace ClaudeDo.Installer.Core;
+
+public static class ScheduledTaskXml
+{
+    public static string Build(string userId, string workerExePath, int restartIntervalMinutes)
+    {
+        var minutes = restartIntervalMinutes < 1 ? 1 : restartIntervalMinutes;
+        var user = SecurityElement.Escape(userId);
+        var cmd = SecurityElement.Escape(workerExePath);
+        return $"""
+        <?xml version="1.0" encoding="UTF-16"?>
+        <Task version="1.4" xmlns="http://schemas.microsoft.com/windows/2004/02/mit/task">
+          <RegistrationInfo>
+            <Description>ClaudeDo background worker (per-user).</Description>
+          </RegistrationInfo>
+          <Triggers>
+            <LogonTrigger>
+              <Enabled>true</Enabled>
+              <UserId>{user}</UserId>
+            </LogonTrigger>
+          </Triggers>
+          <Principals>
+            <Principal id="Author">
+              <UserId>{user}</UserId>
+              <LogonType>InteractiveToken</LogonType>
+              <RunLevel>LeastPrivilege</RunLevel>
+            </Principal>
+          </Principals>
+          <Settings>
+            <MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>
+            <DisallowStartIfOnBatteries>false</DisallowStartIfOnBatteries>
+            <StopIfGoingOnBatteries>false</StopIfGoingOnBatteries>
+            <AllowHardTerminate>true</AllowHardTerminate>
+            <StartWhenAvailable>true</StartWhenAvailable>
+            <Hidden>true</Hidden>
+            <ExecutionTimeLimit>PT0S</ExecutionTimeLimit>
+            <RestartOnFailure>
+              <Interval>PT{minutes}M</Interval>
+              <Count>3</Count>
+            </RestartOnFailure>
+          </Settings>
+          <Actions Context="Author">
+            <Exec>
+              <Command>{cmd}</Command>
+            </Exec>
+          </Actions>
+        </Task>
+        """;
+    }
+}