fix(ssh): prevent orphaned multiplexed connections

Serialize multiplexed SSH master creation per server to avoid concurrent workers spawning orphaned processes. Enable scheduled cleanup for stale mux connections and add guarded orphan process reaping with tests.

app/Console/Kernel.php

@@ -8,6 +8,7 @@ use App\Jobs\CheckHelperImageJob;
 use App\Jobs\CheckTraefikVersionJob;
 use App\Jobs\CleanupInstanceStuffsJob;
 use App\Jobs\CleanupOrphanedPreviewContainersJob;
+use App\Jobs\CleanupStaleMultiplexedConnections;
 use App\Jobs\PullChangelog;
 use App\Jobs\PullTemplatesFromCDN;
 use App\Jobs\RegenerateSslCertJob;
@@ -40,7 +41,7 @@ class Kernel extends ConsoleKernel
             $this->instanceTimezone = config('app.timezone');
         }
 
-        // $this->scheduleInstance->job(new CleanupStaleMultiplexedConnections)->hourly();
+        $this->scheduleInstance->job(new CleanupStaleMultiplexedConnections)->hourly()->onOneServer();
         $this->scheduleInstance->command('cleanup:redis --clear-locks')->daily();
         $this->scheduleInstance->command('sanctum:prune-expired --hours=1')->hourly()->onOneServer();
         $this->scheduleInstance->job(new ApiTokenExpirationWarningJob)->hourly()->onOneServer();