Extract healthcare providers from this medical document. Return a JSON array or null.

Each entry:
- type: "physician", "clinic", "hospital", "therapist"
- value: (empty)
- summary: name + specialty, e.g. "Prof. Dr. Péraud, Neurosurgery"
- data: {"name": "...", "role": "...", "specialty": "...", "institution": "...", "phone": "...", "address": "..."}

Only extract providers who TREATED or REFERRED the patient.
Ignore names from letterheads, board members, administrative staff, or signatories who didn't provide care.

Document:
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