Fix Windows service mode: it could neither start nor stop.

- Start: WinSW's NetX.out.log/err.log in data\runtime are the same files as
  start_netx.ps1's netx.out.log (case-insensitive) and stay open, so NetX
  could not truncate its log and every start failed. WinSW logs now go to
  data\runtime\service.
- Stop: nothing told the service_run.ps1 supervisor to exit, so it kept
  restarting NetX and WinSW waited forever. stop_netx_app.ps1 writes the
  service.stop flag (-KeepSupervisor for the supervisor's own restarts),
  service_run checks it every second, and runtime_ctl / service_lifecycle
  write it before stopping the service.
- WinSW launched powershell.exe as stop hook never reached the script
  (stuck on inherited std handles); run it via cmd with NUL stdin and output
  to data\runtime\service\stopexec.log. stop_netx_app.ps1 keeps a
  timestamped trace there.

Offline Windows Sandbox: service install -> healthy in 28s, stop in 20s.
Existing service installs need "install service" re-run to pick this up.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packaging/service_run.ps1

@@ -57,7 +57,16 @@ function Start-NetxChildren {
 
 function Stop-NetxChildren {
     & powershell.exe -NoProfile -ExecutionPolicy Bypass -File $stopPs1 `
-        -ProgramRoot $prog -DataRoot $data
+        -ProgramRoot $prog -DataRoot $data -KeepSupervisor
+}
+
+function Wait-NetxStopFlag([int]$Seconds) {
+    # Sleep in 1s steps so a service stop (stop flag) is noticed quickly.
+    for ($i = 0; $i -lt $Seconds; $i++) {
+        if (Test-Path $stopFlag) { return $true }
+        Start-Sleep -Seconds 1
+    }
+    return (Test-Path $stopFlag)
 }
 
 try {
@@ -83,11 +92,11 @@ try {
                 Start-NetxChildren
                 $failStreak = 0
                 # Give API time to come up before counting failures again.
-                Start-Sleep -Seconds ([Math]::Max(15, $HealthIntervalSec))
+                $null = Wait-NetxStopFlag ([Math]::Max(15, $HealthIntervalSec))
                 continue
             }
         }
-        Start-Sleep -Seconds $HealthIntervalSec
+        $null = Wait-NetxStopFlag $HealthIntervalSec
     }
 } catch {
     Write-SvcLog "ERROR: $($_.Exception.Message)"