Fix: Remove hardcoded OpenAI API key, use environment variable

- Replace hardcoded API key with environment variable
- Add OPENAI_API_KEY to .env.example for documentation
- Prevents secret exposure in version control

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.env.example

@@ -23,3 +23,6 @@ RESEND_API_KEY=re_your-resend-api-key-here
 # Error Monitoring (Sentry)
 SENTRY_DSN=https://your-sentry-dsn-here@sentry.io/project-id
 SENTRY_RELEASE=1.0.0
+
+# AI Features (OpenAI)
+OPENAI_API_KEY=sk-your-openai-api-key-here