🤖 feat: Latest Grok Model Pricing & Context Rates (#10727)

* 🤖 feat: Latest Grok Model Pricing & Context Rates

- Introduced 'grok-4-fast', 'grok-4-1-fast', and 'grok-code-fast' models with their respective prompt and completion rates.
- Enhanced unit tests to validate prompt and completion rates for the new models, including variations with prefixes.
- Updated token limits for the new models in the tokens utility, ensuring accurate handling in tests.

* 🔧 refactor: Optimize JSON Export Logic in useExportConversation Hook

Updated the export logic to create a Blob from the JSON string before downloading, improving compatibility and performance for file downloads. This change enhances the handling of deeply nested exports while maintaining the file size reduction achieved in previous updates.

packages/api/src/utils/tokens.ts

@@ -280,6 +280,9 @@ const xAIModels = {
   'grok-3-mini': 131072,
   'grok-3-mini-fast': 131072,
   'grok-4': 256000, // 256K context
+  'grok-4-fast': 2000000, // 2M context
+  'grok-4-1-fast': 2000000, // 2M context (covers reasoning & non-reasoning variants)
+  'grok-code-fast': 256000, // 256K context
 };
 
 const aggregateModels = {