Link user to existing OCR transaction
Link a logged-in user to a completed OCR transaction that was created using only an API key (without a user token). This avoids repeating the full three-step capture flow.
**Use case:** Your client-side app performs OCR scanning before the user logs in (using only the `ApiKey`). After the user logs in, call this endpoint to associate the completed verification with their account.
The user is marked **Verified** if the transaction includes valid ID front, ID back, and liveness results — and any required NTRA/CSO checks pass.

