fix(config): update default model version

- Updated the default model from gpt-4.1-mini to gpt-4o-mini.
- Ensured consistency in environment configuration.

The default model version was updated for compatibility with the latest API specifications.

Co-Authored-By: Git Agent <noreply@git-agent.dev>

Author: xesrevinu

src/config/env.ts

@@ -1,7 +1,7 @@
 import { Config, Effect, Option } from "effect";
 
 export const DefaultBaseUrl = "https://api.openai.com/v1";
-export const DefaultModel = "gpt-4.1-mini";
+export const DefaultModel = "gpt-4o-mini";
 export const DefaultGitignoreBaseUrl = "https://www.toptal.com/developers/gitignore/api";
 
 export const envString = (name: string) => Config.string(name);