feat: SuperAdmin server-access kill switch gate

Add /super/settings endpoints and API middleware that returns generic 503 while keeping unlock routes whitelisted.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/Http/Middleware/EnsureSuperAdminRemoteToken.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace App\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+
+/**
+ * Bearer token must match SUPERADMIN_REMOTE_TOKEN (same as SuperAdmin Tenant.remoteApiToken).
+ */
+class EnsureSuperAdminRemoteToken
+{
+    public function handle(Request $request, Closure $next)
+    {
+        $expected = trim((string) config('services.superadmin.remote_token', ''));
+        if ($expected === '') {
+            return response()->json([
+                'message' => 'SUPERADMIN_REMOTE_TOKEN is not configured',
+            ], 503);
+        }
+
+        $auth = (string) $request->header('Authorization', '');
+        $token = '';
+        if (preg_match('/^\s*Bearer\s+(.+)\s*$/i', $auth, $m)) {
+            $token = trim($m[1]);
+        }
+
+        if ($token === '' || ! hash_equals($expected, $token)) {
+            return response()->json(['message' => 'Unauthorized'], 401);
+        }
+
+        return $next($request);
+    }
+}