refactor(i18n): use JSON with flattened key and namespace (#30114)

Co-authored-by: yyh <yuanyouhuilyz@gmail.com>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

web/app/components/datasets/documents/create-from-pipeline/processing/index.spec.tsx

@@ -12,7 +12,10 @@ import Processing from './index'
 // Mock react-i18next (handled by global mock in web/vitest.setup.ts but we override for custom messages)
 vi.mock('react-i18next', () => ({
   useTranslation: () => ({
-    t: (key: string) => key,
+    t: (key: string, options?: { ns?: string }) => {
+      const prefix = options?.ns ? `${options.ns}.` : ''
+      return `${prefix}${key}`
+    },
   }),
 }))