POST /v1/users/user_123/graph/edges
Authorization: Bearer <token>
Content-Type: application/json

{
  "source_id": "11111111-1111-1111-1111-111111111111",
  "target_id": "22222222-2222-2222-2222-222222222222",
  "relation": "RelatedTo",
  "weight": 0.8
}

{
  "status": "accepted"
}