add: background.js for automatic code input

public/manifest.json

@@ -9,6 +9,11 @@
     "tabs",
     "storage"
   ],
+  "background": {
+    "service_worker": "background.js",
+    "type": "module",
+    "scripts": ["background.js"]
+  },
   "action": {
     "default_popup": "index.html"
   },
@@ -17,13 +22,9 @@
   },
   "content_scripts": [
     {
-      "matches": [
-        "https://sso.us.es/*"
-      ],
-      "js": [
-        "scripts/content.js"
-      ],
-      "run_at": "document_idle"
+      "matches": ["https://sso.us.es/*"],
+      "js": ["scripts/content.js"],
+      "run_at": "document_start"
     }
   ],
   "host_permissions": [