Create AI conversation

Creates a new AI conversation.

POST /api/sonar/ai/conversations

curl -H "Authorization: Bearer <API_KEY>" \
     -X POST \
     https://HOSTNAME/api/sonar/ai/conversations

{
  "guid": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "title": "New conversation"
}