feat(i18n): add missing i18n keys for knowledge validation messages

Add engineSettingsInvalid and retrievalSettingsInvalid keys to all
locale files (zh-Hant, ja-JP, vi-VN, es-ES, ru-RU, th-TH) for the
new dynamic form validation feature.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

web/src/i18n/locales/zh-Hant.ts

@@ -880,6 +880,8 @@ const zhHant = {
     engineSettings: '引擎設定',
     engineSettingsDescription: '所選知識引擎的設定',
     engineSettingsReadonly: '編輯模式下不可修改',
+    engineSettingsInvalid: '引擎設定中存在無效項，請檢查必填欄位',
+    retrievalSettingsInvalid: '檢索設定中存在無效項，請檢查必填欄位',
     retrievalSettings: '檢索設定',
     retrievalSettingsDescription: '設定從此知識庫檢索文件的方式',
     dangerZone: '危險區域',