feat(i18n): add Kazakh translation (#14981)

Closes #14975

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## Summary by CodeRabbit

* **New Features**
* Kazakh (kk) language has been added — users can now choose Kazakh for
the interface, with complete localization coverage and language metadata
(name and flag) included.

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packages/frontend/i18n/src/i18n-completenesses.json

@@ -13,6 +13,7 @@
   "hi": 1,
   "it": 94,
   "ja": 93,
+  "kk": 100,
   "ko": 93,
   "nb-NO": 46,
   "pl": 94,