Move maintenance guard infrastructure into VG-Core

manifest.json

@@ -29,7 +29,7 @@
     "src/background/db/db-record-locks.js",
     "src/background/utils.js",
     "src/background/settings.js",
-    "src/background/maintenance-guard.js",
+    "src/core/maintenance-guard.js",
     "src/background/consent-memory.js",
     "src/background/request-fingerprint.js",
     "src/background/request-observer.js",