fix(acp): pin @latest for all plugins and enable button when only floating versions exist

- install_missing_plugins now pins ALL @latest specs (not just newly installed)
- When nothing is missing but @latest exists, the pin-only path runs
- Modal button switches to 'Pin @latest Versions' when no missing plugins
- Added pinVersions i18n key for 10 languages

src/i18n/messages/ar.json

@@ -695,6 +695,7 @@
         "missing": "غير مثبّت"
       },
       "installAll": "تثبيت جميع الإضافات المفقودة",
+      "pinVersions": "تثبيت إصدارات @latest",
       "install": "تثبيت",
       "uninstall": "إزالة",
       "refresh": "تحديث",