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/ja.json

@@ -695,6 +695,7 @@
         "missing": "未インストール"
       },
       "installAll": "不足プラグインをすべてインストール",
+      "pinVersions": "@latest バージョンを固定",
       "install": "インストール",
       "uninstall": "アンインストール",
       "refresh": "更新",