fix(engine): honour configured WireGuard prefix length in wg0.conf

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

app/Provisioning/Steps/Host/ConfigureWireguard.php

@@ -8,6 +8,7 @@ use App\Provisioning\StepResult;
 use App\Services\Ssh\RemoteShell;
 use App\Services\Wireguard\WireguardHub;
 use Illuminate\Support\Facades\Cache;
+use Illuminate\Support\Str;
 
 /**
  * Installs WireGuard on the host, allocates a management IP, registers the host
@@ -74,10 +75,11 @@ class ConfigureWireguard extends HostStep
     private function renderConfig(string $wgIp, string $privateKey): string
     {
         $subnet = (string) config('provisioning.wireguard.subnet', '10.66.0.0/24');
+        $prefix = Str::afterLast($subnet, '/'); // honour the configured prefix length
 
         return implode("\n", [
             '[Interface]',
-            "Address = {$wgIp}/24",
+            "Address = {$wgIp}/{$prefix}",
             "PrivateKey = {$privateKey}",
             '',
             '[Peer]',