INC-4821 · Record update rejected after media-type migration

Endpoint requirement
--------------------
PATCH /v1/records/{record_id}
Content-Type: application/merge-patch+json
Body fields:
- state: draft | in_review | closed
- notify: boolean

Reproduction used by the client team
------------------------------------
curl --include --request PATCH \
  'https://records.internal.example/v1/records/REC-204' \
  --header 'Accept: application/json' \
  --header 'Content-Type: application/json' \
  --data '{"state":"in_review","notify":false}'

Observed response
-----------------
HTTP/1.1 415 Unsupported Media Type
Content-Type: application/problem+json
Content-Length: 108
X-Request-ID: req-8f21

{"title":"Unsupported Media Type","status":415,"detail":"Content-Type must be application/merge-patch+json"}