Service: --run-service host + registration CLI (install/uninstall/start/stop)

Local checkpoint - NOT for public release.

- RemSoundService (ServiceBase): hosts ServiceSendHost.RunLoop on a worker thread,
  OnStop cancels + joins. Added System.ServiceProcess.ServiceController package.
- ServiceControl: install (sc.exe create, auto-start, careful binPath quoting) /
  uninstall (stop + delete) / start / stop / status. Status query is unprivileged
  (menu can poll it); the mutating verbs self-elevate via ShellExecute runas.
- Program.cs: early guards for --run-service (blocks in the SCM dispatcher) and the
  one-shot elevated verbs, before the single-instance lock (the service is a
  separate role and must never take the interactive lock).
- Self-test "Service registration args" verifies the sc create binPath quoting
  survives a spaced exe path. Gate 20/20.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/RemSound.App/RemSoundService.cs

@@ -0,0 +1,66 @@
+using System.ServiceProcess;
+using RemSound.Core;
+
+namespace RemSound.App;
+
+/// <summary>
+/// The RemSound Windows service (send-only lock-screen streaming). Hosts <see cref="ServiceSendHost"/>
+/// on a background thread; the host's own RunLoop yields to the interactive app via
+/// <see cref="InteractivePresence"/>. Started by the SCM when Program.cs is launched with
+/// <see cref="ServiceControl.RunVerb"/>.
+/// </summary>
+public sealed class RemSoundService : ServiceBase
+{
+    private readonly CancellationTokenSource cts = new();
+    private Thread? worker;
+    private ServiceSendHost? host;
+    private RemSoundLog? log;
+
+    public RemSoundService()
+    {
+        ServiceName = ServiceControl.ServiceName;
+        CanStop = true;
+        CanShutdown = true;
+        CanPauseAndContinue = false;
+    }
+
+    protected override void OnStart(string[] args)
+    {
+        log = new RemSoundLog { Enabled = SafeServiceLogging() };
+        log.Event("service: OnStart");
+        host = ServiceSendHost.FromConfig(msg => log?.Event(msg));
+        worker = new Thread(() =>
+        {
+            try { host.RunLoop(cts.Token); }
+            catch (Exception ex) { log?.Event($"service: run loop crashed {ex.GetType().Name}: {ex.Message}"); }
+        })
+        { IsBackground = true, Name = "remsound-service" };
+        worker.Start();
+    }
+
+    protected override void OnStop()
+    {
+        log?.Event("service: OnStop");
+        try { cts.Cancel(); } catch { }
+        try { worker?.Join(5000); } catch { }
+        try { host?.Dispose(); } catch { }
+    }
+
+    protected override void OnShutdown() => OnStop();
+
+    private static bool SafeServiceLogging()
+    {
+        try { return AppConfig.Load().ServiceLoggingEnabled; }
+        catch { return false; }
+    }
+
+    protected override void Dispose(bool disposing)
+    {
+        if (disposing) { try { cts.Dispose(); } catch { } }
+        base.Dispose(disposing);
+    }
+
+    /// <summary>Blocks in the SCM dispatcher until the service is stopped. Called from Program.cs
+    /// when launched with the run verb.</summary>
+    public static void RunAsService() => ServiceBase.Run(new RemSoundService());
+}