Add GPT-4o mini support

Reference:
- https://platform.openai.com/docs/models/gpt-4o-mini
- https://openai.com/index/gpt-4o-mini-advancing-cost-efficient-intelligence/

app/constant.ts

@@ -182,6 +182,8 @@ export const KnowledgeCutOffDate: Record<string, string> = {
   "gpt-4-turbo-preview": "2023-12",
   "gpt-4o": "2023-10",
   "gpt-4o-2024-05-13": "2023-10",
+  "gpt-4o-mini": "2023-10",
+  "gpt-4o-mini-2024-07-18": "2023-10",
   "gpt-4-vision-preview": "2023-04",
   // After improvements,
   // it's now easier to add "KnowledgeCutOffDate" instead of stupid hardcoding it, as was done previously.
@@ -201,6 +203,8 @@ const openaiModels = [
   "gpt-4-turbo-preview",
   "gpt-4o",
   "gpt-4o-2024-05-13",
+  "gpt-4o-mini",
+  "gpt-4o-mini-2024-07-18",
   "gpt-4-vision-preview",
   "gpt-4-turbo-2024-04-09",
   "gpt-4-1106-preview",