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,

packages/frontend/i18n/src/resources/index.ts

@@ -23,7 +23,8 @@ export type Language =
   | 'ko'
   | 'pt-BR'
   | 'fa'
-  | 'nb-NO';
+  | 'nb-NO'
+  | 'kk';
 
 export type LanguageResource = typeof en;
 export const SUPPORTED_LANGUAGES: Record<
@@ -179,4 +180,10 @@ export const SUPPORTED_LANGUAGES: Record<
     flagEmoji: '🇳🇴',
     resource: () => import('./nb-NO.json'),
   },
+  kk: {
+    name: 'Kazakh',
+    originalName: 'Қазақша',
+    flagEmoji: '🇰🇿',
+    resource: () => import('./kk.json'),
+  },
 };